Fix rd_pick_partition search loop for 4x4 blocks

The partition search for 4x4 blocks takes unnecessary steps to
reconstruct pixels and an extra partition type update. This commit
removes such operations. No visible compression/speed difference.
Thanks to Yue (yuec@) for finding this issue.

Change-Id: I3f83824aa3fd3717d63be0b280fa57258939a70a

vp9/encoder/vp9_encodeframe.c

@@ -2015,17 +2015,10 @@ static void rd_pick_partition(VP9_COMP *cpi, const TileInfo *const tile,
             ctx->mic.mbmi.interp_filter;
       rd_pick_sb_modes(cpi, tile, mi_row, mi_col, &sum_rate, &sum_dist, subsize,
                        pc_tree->leaf_split[0], best_rd, 0);
-      if (sum_rate == INT_MAX) {
+      if (sum_rate == INT_MAX)
         sum_rd = INT64_MAX;
-      } else {
+      else
         sum_rd = RDCOST(x->rdmult, x->rddiv, sum_rate, sum_dist);
-        if (sum_rd < best_rd) {
-          update_state(cpi, pc_tree->leaf_split[0], mi_row, mi_col, subsize, 0);
-          encode_superblock(cpi, tp, 0, mi_row, mi_col, subsize,
-                            pc_tree->leaf_split[0]);
-          update_partition_context(xd, mi_row, mi_col, subsize, bsize);
-        }
-      }
     } else {
       for (i = 0; i < 4 && sum_rd < best_rd; ++i) {
       const int x_idx = (i & 1) * mi_step;