Remove TOTAL_REFS_PER_FRAME

In the codebase, TOTAL_REFS_PER_FRAME in fact completely overlaps
with REF_FRAMES, as both are valued 8 and both indicate the maximum
total number of reference frames that can be buffered and then can
be used for each inter coded frame. This CL keeps REF_FRAMES and
removes TOTAL_REFS_PER_FRAME to avoid unnecessary confusion due to
duplicate definitions.

Change-Id: Ia9761194d7223cc7d3c1a974bf7b782c06e8b224
diff --git a/av1/encoder/rd.h b/av1/encoder/rd.h
index c67d054..47194d4 100644
--- a/av1/encoder/rd.h
+++ b/av1/encoder/rd.h
@@ -282,7 +282,7 @@
 
   int threshes[MAX_SEGMENTS][BLOCK_SIZES_ALL][MAX_MODES];
 
-  int64_t prediction_type_threshes[TOTAL_REFS_PER_FRAME][REFERENCE_MODES];
+  int64_t prediction_type_threshes[REF_FRAMES][REFERENCE_MODES];
 
   int RDMULT;
 } RD_OPT;