memtx: remove dead code

The function memtx_tx_story_delete is expected to delete fully
unlinked stories and thus should not try to unlink something by
itself. So remove unlink and add asserts instead.

Part of #8648
Part of #8654

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring

(cherry picked from commit 07067407)

src/box/memtx_tx.c

@@ -937,24 +937,19 @@ memtx_tx_story_new(struct space *space, struct tuple *tuple)
 static void
 memtx_tx_story_delete(struct memtx_story *story)
 {
+	/* Expecting to delete fully unlinked story. */
+	assert(story->add_stmt == NULL);
+	assert(story->del_stmt == NULL);
+	for (uint32_t i = 0; i < story->index_count; i++) {
+		assert(story->link[i].newer_story == NULL);
+		assert(story->link[i].older_story == NULL);
+	}
+
 	memtx_tx_stats_discard(&txm.story_stats[story->status],
 			       memtx_story_size(story));
 	if (story->tuple_is_retained)
 		memtx_tx_story_untrack_retained_tuple(story);
 
-	if (story->add_stmt != NULL) {
-		assert(story->add_stmt->add_story == story);
-		story->add_stmt->add_story = NULL;
-		story->add_stmt = NULL;
-	}
-	while (story->del_stmt != NULL) {
-		assert(story->del_stmt->del_story == story);
-		story->del_stmt->del_story = NULL;
-		struct txn_stmt *next = story->del_stmt->next_in_del_list;
-		story->del_stmt->next_in_del_list = NULL;
-		story->del_stmt = next;
-	}
-
 	if (txm.traverse_all_stories == &story->in_all_stories)
 		txm.traverse_all_stories = rlist_next(txm.traverse_all_stories);
 	rlist_del(&story->in_all_stories);
@@ -967,14 +962,6 @@ memtx_tx_story_delete(struct memtx_story *story)
 	tuple_clear_flag(story->tuple, TUPLE_IS_DIRTY);
 	tuple_unref(story->tuple);
 
-#ifndef NDEBUG
-	/* Expecting to delete fully unlinked story. */
-	for (uint32_t i = 0; i < story->index_count; i++) {
-		assert(story->link[i].newer_story == NULL);
-		assert(story->link[i].older_story == NULL);
-	}
-#endif
-
 	struct mempool *pool = &txm.memtx_tx_story_pool[story->index_count];
 	mempool_free(pool, story);
 }