Revert "[NORMATIVE] Allow IDTX for chroma in some cases"

This reverts commit c341ea8990025994b8680c9cc7237cc2be66a2c4.

Reason for revert: As decided in codec WG.

Change-Id: Ice24112482d04445d16ac9e237615512969a847d

av1/common/blockd.h

diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index 4e0e2dc..c579d98 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -847,12 +847,7 @@
     } else {
       // In intra mode, uv planes don't share the same prediction mode as y
       // plane, so the tx_type should not be shared
-      const int txk_type_idx =
-          av1_get_txk_type_index(mbmi->sb_type, blk_row, blk_col);
-      tx_type = mbmi->txk_type[txk_type_idx];
-      if (!(tx_type == IDTX && mbmi->mode == DC_PRED &&
-            mbmi->uv_mode == UV_DC_PRED))
-        tx_type = intra_mode_to_tx_type(mbmi, PLANE_TYPE_UV);
+      tx_type = intra_mode_to_tx_type(mbmi, PLANE_TYPE_UV);
     }
   }
   assert(tx_type < TX_TYPES);