memtx: drop memtx_tx_track_read_story_slow

The only place where this static function is used is more general
static function - memtx_tx_track_read_story. This is a bit
confusing - usually slow variant stand for public inline 'fast'
method.

So merge both functions in one.

Part of tarantool#8648
Part of tarantool#8654

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

src/box/memtx_tx.c

@@ -2663,9 +2663,16 @@ tx_read_tracker_new(struct txn *reader, struct memtx_story *story,
 }
 
 static void
-memtx_tx_track_read_story_slow(struct txn *txn, struct memtx_story *story,
-			       uint64_t index_mask)
+memtx_tx_track_read_story(struct txn *txn, struct space *space,
+			  struct memtx_story *story, uint64_t index_mask)
 {
+	if (txn == NULL)
+		return;
+	if (space == NULL)
+		return;
+	if (space->def->opts.is_ephemeral)
+		return;
+	(void)space;
 	assert(story != NULL);
 	struct tx_read_tracker *tracker = NULL;
 
@@ -2698,19 +2705,6 @@ memtx_tx_track_read_story_slow(struct txn *txn, struct memtx_story *story,
 	rlist_add(&txn->read_set, &tracker->in_read_set);
 }
 
-static void
-memtx_tx_track_read_story(struct txn *txn, struct space *space,
-			  struct memtx_story *story, uint64_t index_mask)
-{
-	if (txn == NULL)
-		return;
-	if (space == NULL)
-		return;
-	if (space->def->opts.is_ephemeral)
-		return;
-	memtx_tx_track_read_story_slow(txn, story, index_mask);
-}
-
 /**
  * Record in TX manager that a transaction @txn have read a @tuple in @space.
  *