blk-mq: don't check queue mapped in __blk_mq_delay_run_hw_queue()

There are several reasons for removing the check:

1) blk_mq_hw_queue_mapped() returns true always now since each hctx
may be mapped by one CPU at least

2) when there isn't any online CPU mapped to this hctx, there won't
be any IO queued to this CPU, blk_mq_run_hw_queue() only runs queue
if there is IO queued to this hctx

3) If __blk_mq_delay_run_hw_queue() is called by blk_mq_delay_run_hw_queue(),
which is run from blk_mq_dispatch_rq_list() or scsi_mq_get_budget(), and
the hctx to be handled has to be mapped.

Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Tested-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -1393,9 +1393,6 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
 static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 					unsigned long msecs)
 {
-	if (WARN_ON_ONCE(!blk_mq_hw_queue_mapped(hctx)))
-		return;
-
 	if (unlikely(blk_mq_hctx_stopped(hctx)))
 		return;