block: remove inaccurate requeue check

This check is meant to catch cases where a requeue is attempted on a
request that is still inserted. It's never really been useful to catch any
misuse, and now it's actively wrong. Outside of that, this should not be a
BUG_ON() to begin with.

Remove the check as it's now causing active harm, as requeue off the plug
path will trigger it even though the request state is just fine.
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Link: https://lore.kernel.org/linux-block/CAHj4cs80zAUc2grnCZ015-2Rvd-=gXRfB_dFKy=RTm+wRo09HQ@mail.gmail.com/Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -1053,7 +1053,6 @@ void blk_mq_requeue_request(struct request *rq, bool kick_requeue_list)
 	/* this request will be re-inserted to io scheduler queue */
 	blk_mq_sched_requeue_request(rq);
 
-	BUG_ON(!list_empty(&rq->queuelist));
 	blk_mq_add_to_requeue_list(rq, true, kick_requeue_list);
 }
 EXPORT_SYMBOL(blk_mq_requeue_request);