[non-normative, segment-pred-last] Remove duplicate code block

There is some code to initialize cm->last_frame_seg_map, which is
run *before* we decide if segmentation is enabled for the current
frame. Thus we set up the map based on the *previous decoded frame's*
value of cm->seg.enabled.

Further, once we have read cm->seg.enabled, we have another identical
code block, which always overwrites the values set by the first block.
Thus we can delete this first code block.

This should cause no change in behaviour.

BUG=aomedia:1332

Change-Id: I0354403f9b932aa3fa56f4954b7b6cca34927812

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index b884465..9a10693 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -3031,15 +3031,6 @@
               : NULL;
       cm->use_prev_frame_mvs =
           cm->use_ref_frame_mvs && frame_can_use_prev_frame_mvs(cm);
-#if CONFIG_SEGMENT_PRED_LAST
-      if (cm->seg.enabled && !cm->frame_parallel_decode && cm->prev_frame &&
-          (cm->mi_rows == cm->prev_frame->mi_rows) &&
-          (cm->mi_cols == cm->prev_frame->mi_cols)) {
-        cm->last_frame_seg_map = cm->prev_frame->seg_map;
-      } else {
-        cm->last_frame_seg_map = NULL;
-      }
-#endif
       for (int i = 0; i < INTER_REFS_PER_FRAME; ++i) {
         RefBuffer *const ref_buf = &cm->frame_refs[i];
         av1_setup_scale_factors_for_frame(