Cleanup RD_RECORD_IDX_NODE structure

This CL removes the definition of unused structure
RD_RECORD_IDX_NODE. This CL also reintroduces the
assert that was removed in the CL below.
https://aomedia-review.googlesource.com/c/aom/+/146161

Change-Id: I105220839eddb9668198e1e786623866a3691f33

av1/encoder/tx_search.c

diff --git a/av1/encoder/tx_search.c b/av1/encoder/tx_search.c
index a3ac0d9..b02ccef 100644
--- a/av1/encoder/tx_search.c
+++ b/av1/encoder/tx_search.c
@@ -44,11 +44,6 @@
   TX_TYPE tx_type;
 } TxCandidateInfo;
 
-typedef struct {
-  int leaf;
-  int8_t children[4];
-} RD_RECORD_IDX_NODE;
-
 // origin_threshold * 128 / 100
 static const uint32_t skip_pred_threshold[3][BLOCK_SIZES_ALL] = {
   {
@@ -2270,6 +2265,7 @@
                                   RD_STATS *rd_stats,
                                   FAST_TX_SEARCH_MODE ftxs_mode,
                                   int64_t ref_rdcost) {
+  assert(is_inter_block(x->e_mbd.mi[0]));
   RD_STATS this_rd_stats;
   const int skip_trellis = 0;
   search_tx_type(cpi, x, 0, block, blk_row, blk_col, plane_bsize, tx_size,