Remove CONFIG_MODIFY_SH macro

on item in https://gitlab.com/AOMediaCodec/avm/-/issues/1076
diff --git a/av2/av2_dx_iface.c b/av2/av2_dx_iface.c
index 6e28c2f..a359604 100644
--- a/av2/av2_dx_iface.c
+++ b/av2/av2_dx_iface.c
@@ -366,9 +366,6 @@
                                               avm_codec_stream_info_t *si) {
   int operating_point_idc0 = 0;
   if (is_reduced_header) {
-#if !CONFIG_MODIFY_SH
-    avm_rb_read_literal(rb, LEVEL_BITS);  // level
-#endif                                    // !CONFIG_MODIFY_SH
   } else {
     uint8_t decoder_model_info_present_flag = 0;
     int buffer_delay_length_minus_1 = 0;
@@ -394,10 +391,6 @@
       int operating_point_idc;
       operating_point_idc = avm_rb_read_literal(rb, OP_POINTS_IDC_BITS);
       if (i == 0) operating_point_idc0 = operating_point_idc;
-#if !CONFIG_MODIFY_SH
-      int seq_level_idx = avm_rb_read_literal(rb, LEVEL_BITS);  // level
-      if (seq_level_idx > 7) avm_rb_read_bit(rb);               // tier
-#endif  // !CONFIG_MODIFY_SH
       if (decoder_model_info_present_flag) {
         const uint8_t decoder_model_present_for_this_op = avm_rb_read_bit(rb);
         if (decoder_model_present_for_this_op) {
@@ -476,7 +469,6 @@
 #endif                        // CONFIG_CWG_E242_SEQ_HDR_ID
 
       BITSTREAM_PROFILE profile = av2_read_profile(&rb);  // profile
-#if CONFIG_MODIFY_SH
       single_picture_header_flag = avm_rb_read_bit(&rb);
       if (!single_picture_header_flag) {
         avm_rb_read_literal(&rb, 3);  // seq_lcr_id
@@ -486,9 +478,6 @@
           avm_rb_read_literal(&rb, LEVEL_BITS);  // seq_level_idx
       if (seq_level_idx > 7 && !single_picture_header_flag)
         avm_rb_read_bit(&rb);  // seq_tier_flag
-#else
-      avm_rb_read_literal(&rb, 3);
-#endif  // CONFIG_MODIFY_SH
 
       int num_bits_width = avm_rb_read_literal(&rb, 4) + 1;
       int num_bits_height = avm_rb_read_literal(&rb, 4) + 1;
@@ -514,15 +503,6 @@
 #endif  // CONFIG_CWG_F270_CI_OBU
       if (status != AVM_CODEC_OK) return status;
 
-#if !CONFIG_MODIFY_SH
-      const uint8_t still_picture = avm_rb_read_bit(&rb);
-      single_picture_header_flag = avm_rb_read_bit(&rb);
-
-      if (!still_picture && single_picture_header_flag) {
-        return AVM_CODEC_UNSUP_BITSTREAM;
-      }
-#endif  // !CONFIG_MODIFY_SH
-
 #if !CONFIG_CWG_F270_OPS
       status = parse_operating_points(&rb, single_picture_header_flag, si);
       if (status != AVM_CODEC_OK) return status;
diff --git a/av2/decoder/obu.c b/av2/decoder/obu.c
index 6d0d40e..916f36c 100644
--- a/av2/decoder/obu.c
+++ b/av2/decoder/obu.c
@@ -276,7 +276,6 @@
     return 0;
   }
 #endif  // !CONFIG_CWG_F270_OPS
-#if CONFIG_MODIFY_SH
   seq_params->single_picture_header_flag = avm_rb_read_bit(rb);
   if (seq_params->single_picture_header_flag) {
     seq_params->seq_lcr_id = LCR_ID_UNSPECIFIED;
@@ -311,7 +310,6 @@
   else
     seq_params->tier[0] = 0;
 #endif  // CONFIG_CWG_F270_OPS
-#endif  // CONFIG_MODIFY_SH
 
   const int num_bits_width = avm_rb_read_literal(rb, 4) + 1;
   const int num_bits_height = avm_rb_read_literal(rb, 4) + 1;
@@ -345,17 +343,6 @@
   }
 #endif  // !CONFIG_CWG_E242_CHROMA_FORMAT_IDC
 
-#if !CONFIG_MODIFY_SH
-  // Still picture or not
-  seq_params->still_picture = avm_rb_read_bit(rb);
-  seq_params->single_picture_header_flag = avm_rb_read_bit(rb);
-  // Video must have single_picture_header_flag = 0
-  if (!seq_params->still_picture && seq_params->single_picture_header_flag) {
-    cm->error.error_code = AVM_CODEC_UNSUP_BITSTREAM;
-    return 0;
-  }
-#endif  // !CONFIG_MODIFY_SH
-
 #if CONFIG_CWG_F270_OPS
   if (seq_params->single_picture_header_flag) {
     seq_params->decoder_model_info_present_flag = 0;
@@ -410,13 +397,6 @@
     seq_params->display_model_info_present_flag = 0;
     seq_params->operating_points_cnt_minus_1 = 0;
     seq_params->operating_point_idc[0] = 0;
-#if !CONFIG_MODIFY_SH
-    if (!read_bitstream_level(&seq_params->seq_level_idx[0], rb)) {
-      cm->error.error_code = AVM_CODEC_UNSUP_BITSTREAM;
-      return 0;
-    }
-    seq_params->tier[0] = 0;
-#endif  // !CONFIG_MODIFY_SH
     seq_params->op_params[0].decoder_model_param_present_flag = 0;
     seq_params->op_params[0].display_model_param_present_flag = 0;
   } else {
@@ -439,18 +419,6 @@
     for (int i = 0; i < seq_params->operating_points_cnt_minus_1 + 1; i++) {
       seq_params->operating_point_idc[i] =
           avm_rb_read_literal(rb, OP_POINTS_IDC_BITS);
-#if !CONFIG_MODIFY_SH
-      if (!read_bitstream_level(&seq_params->seq_level_idx[i], rb)) {
-        cm->error.error_code = AVM_CODEC_UNSUP_BITSTREAM;
-        return 0;
-      }
-      // This is the seq_level_idx[i] > 7 check in the spec. seq_level_idx 7
-      // is equivalent to level 3.3.
-      if (seq_params->seq_level_idx[i] >= SEQ_LEVEL_4_0)
-        seq_params->tier[i] = avm_rb_read_bit(rb);
-      else
-        seq_params->tier[i] = 0;
-#endif  // !CONFIG_MODIFY_SH
       if (seq_params->decoder_model_info_present_flag) {
         seq_params->op_params[i].decoder_model_param_present_flag =
             avm_rb_read_bit(rb);
diff --git a/av2/encoder/bitstream.c b/av2/encoder/bitstream.c
index d97d377..e8f26a9 100644
--- a/av2/encoder/bitstream.c
+++ b/av2/encoder/bitstream.c
@@ -7378,7 +7378,6 @@
 #endif  // CONFIG_CWG_E242_SEQ_HDR_ID
 
   write_profile(seq_params->profile, &wb);
-#if CONFIG_MODIFY_SH
   avm_wb_write_bit(&wb, seq_params->single_picture_header_flag);
   if (!seq_params->single_picture_header_flag) {
     avm_wb_write_literal(&wb, seq_params->seq_lcr_id, 3);
@@ -7395,7 +7394,6 @@
       !seq_params->single_picture_header_flag)
     avm_wb_write_bit(&wb, seq_params->tier[0]);
 #endif  // CONFIG_CWG_F270_OPS
-#endif  // CONFIG_MODIFY_SH
 
   avm_wb_write_literal(&wb, seq_params->num_bits_width - 1, 4);
   avm_wb_write_literal(&wb, seq_params->num_bits_height - 1, 4);
@@ -7414,24 +7412,12 @@
   write_color_config(seq_params, &wb);
 #endif  // CONFIG_CWG_F270_CI_OBU
 
-#if !CONFIG_MODIFY_SH
-  // Still picture or not
-  avm_wb_write_bit(&wb, seq_params->still_picture);
-  assert(IMPLIES(!seq_params->still_picture,
-                 !seq_params->single_picture_header_flag));
-  // whether to use reduced still picture header
-  avm_wb_write_bit(&wb, seq_params->single_picture_header_flag);
-#endif  // !CONFIG_MODIFY_SH
-
   if (seq_params->single_picture_header_flag) {
 #if !CONFIG_CWG_F270_CI_OBU
     assert(seq_params->timing_info_present == 0);
 #endif  // !CONFIG_CWG_F270_CI_OBU
     assert(seq_params->decoder_model_info_present_flag == 0);
     assert(seq_params->display_model_info_present_flag == 0);
-#if !CONFIG_MODIFY_SH
-    write_bitstream_level(seq_params->seq_level_idx[0], &wb);
-#endif  // !CONFIG_MODIFY_SH
   } else {
 #if CONFIG_CWG_F270_OPS
     avm_wb_write_bit(&wb, seq_params->seq_max_display_model_info_present_flag);
@@ -7473,11 +7459,6 @@
     for (i = 0; i < seq_params->operating_points_cnt_minus_1 + 1; i++) {
       avm_wb_write_literal(&wb, seq_params->operating_point_idc[i],
                            OP_POINTS_IDC_BITS);
-#if !CONFIG_MODIFY_SH
-      write_bitstream_level(seq_params->seq_level_idx[i], &wb);
-      if (seq_params->seq_level_idx[i] >= SEQ_LEVEL_4_0)
-        avm_wb_write_bit(&wb, seq_params->tier[i]);
-#endif  // !CONFIG_MODIFY_SH
       if (seq_params->decoder_model_info_present_flag) {
         avm_wb_write_bit(
             &wb, seq_params->op_params[i].decoder_model_param_present_flag);
diff --git a/build/cmake/avm_config_defaults.cmake b/build/cmake/avm_config_defaults.cmake
index 5568fae..9c52044 100644
--- a/build/cmake/avm_config_defaults.cmake
+++ b/build/cmake/avm_config_defaults.cmake
@@ -171,9 +171,6 @@
 
 set_avm_config_var(CONFIG_CWG_E242_SEQ_HDR_ID 1 "Signal sequence header id.")
 
-set_avm_config_var(CONFIG_MODIFY_SH 1
-                   "Modification to the sequence header elements.")
-
 set_avm_config_var(CONFIG_REORDER_SEQ_FLAGS 1 "Group sequence header flags.")
 set_avm_config_var(CONFIG_IMPROVED_REORDER_SEQ_FLAGS 1
                    "Improvement of Group sequence header flags.")
diff --git a/common/av2_config.c b/common/av2_config.c
index 443d7c4..6782101 100644
--- a/common/av2_config.c
+++ b/common/av2_config.c
@@ -366,7 +366,6 @@
 
   AV2C_READ_BITS_OR_RETURN_ERROR(seq_profile, 3);
   config->seq_profile = seq_profile;
-#if CONFIG_MODIFY_SH
   AV2C_READ_BIT_OR_RETURN_ERROR(single_picture_header_flag);
   if (!single_picture_header_flag) {
     AV2C_READ_BITS_OR_RETURN_ERROR(seq_lcr_id, 3);
@@ -379,7 +378,6 @@
     AV2C_READ_BIT_OR_RETURN_ERROR(single_tier_0);
     config->seq_tier_0 = 0;
   }
-#endif  // CONFIG_MODIFY_SH
 
   AV2C_READ_BITS_OR_RETURN_ERROR(frame_width_bits_minus_1, 4);
   AV2C_READ_BITS_OR_RETURN_ERROR(frame_height_bits_minus_1, 4);
@@ -417,17 +415,8 @@
   }
 #endif  // CONFIG_CWG_F270_CI_OBU
 
-#if !CONFIG_MODIFY_SH
-  AV2C_READ_BIT_OR_RETURN_ERROR(still_picture);
-  AV2C_READ_BIT_OR_RETURN_ERROR(single_picture_header_flag);
-#endif  // !CONFIG_MODIFY_SH
   if (single_picture_header_flag) {
     config->initial_presentation_delay_present = 0;
-#if !CONFIG_MODIFY_SH
-    AV2C_READ_BITS_OR_RETURN_ERROR(seq_level_idx, 5);
-    config->seq_level_idx_0 = seq_level_idx;
-    config->seq_tier_0 = 0;
-#endif  // !CONFIG_MODIFY_SH
   } else {
 #if CONFIG_CWG_F270_OPS
     AV2C_READ_BIT_OR_RETURN_ERROR(max_display_model_info_present_flag);
@@ -487,15 +476,6 @@
 
     for (int op_index = 0; op_index < num_operating_points; ++op_index) {
       AV2C_READ_BITS_OR_RETURN_ERROR(operating_point_idc, 12);
-#if !CONFIG_MODIFY_SH
-      AV2C_READ_BITS_OR_RETURN_ERROR(seq_level_idx, 5);
-
-      int seq_tier = 0;
-      if (seq_level_idx > 7) {
-        AV2C_READ_BIT_OR_RETURN_ERROR(seq_tier_this_op);
-        seq_tier = seq_tier_this_op;
-      }
-#endif  // !CONFIG_MODIFY_SH
       if (has_decoder_model) {
         AV2C_READ_BIT_OR_RETURN_ERROR(decoder_model_present_for_op);
         if (decoder_model_present_for_op) {
@@ -519,10 +499,6 @@
 
       if (op_index == 0) {
         // Av2Config needs only the values from the first operating point.
-#if !CONFIG_MODIFY_SH
-        config->seq_level_idx_0 = seq_level_idx;
-        config->seq_tier_0 = seq_tier;
-#endif  // !CONFIG_MODIFY_SH
         config->initial_presentation_delay_present = 0;
         config->initial_presentation_delay_minus_one = 0;
       }