Take out drl index control from opt-ref-mv

Removing the drl dependency on the candidate list length appears
to incur more than 0.3% compression performance loss. Hence remove
this option from opt-ref-mv to allow better latency vs compression
performance trade off.

Change-Id: I6edaeb2d437996082b7bdd6cda7351426c5584b9

av1/encoder/bitstream.c

diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 1ecca53..dda3372 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -148,8 +148,7 @@
   if (new_mv) {
     int idx;
     for (idx = 0; idx < 2; ++idx) {
-      if (mbmi_ext->ref_mv_count[ref_frame_type] > idx + 1 ||
-          CONFIG_OPT_REF_MV) {
+      if (mbmi_ext->ref_mv_count[ref_frame_type] > idx + 1) {
         uint8_t drl_ctx =
             av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], idx);
 
@@ -165,8 +164,7 @@
     int idx;
     // TODO(jingning): Temporary solution to compensate the NEARESTMV offset.
     for (idx = 1; idx < 3; ++idx) {
-      if (mbmi_ext->ref_mv_count[ref_frame_type] > idx + 1 ||
-          CONFIG_OPT_REF_MV) {
+      if (mbmi_ext->ref_mv_count[ref_frame_type] > idx + 1) {
         uint8_t drl_ctx =
             av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], idx);
         aom_write_symbol(w, mbmi->ref_mv_idx != (idx - 1),