block: get rid of unused plug->nowait flag

This was introduced to add a plug based way of signaling nowait issues,
but we have since moved on from that. Kill the old dead code, nobody is
setting it anymore.
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -722,14 +722,9 @@ void submit_bio_noacct(struct bio *bio)
 	struct block_device *bdev = bio->bi_bdev;
 	struct request_queue *q = bdev_get_queue(bdev);
 	blk_status_t status = BLK_STS_IOERR;
-	struct blk_plug *plug;
 
 	might_sleep();
 
-	plug = blk_mq_plug(bio);
-	if (plug && plug->nowait)
-		bio->bi_opf |= REQ_NOWAIT;
-
 	/*
 	 * For a REQ_NOWAIT based request, return -EOPNOTSUPP
 	 * if queue does not support NOWAIT.
@@ -1059,7 +1054,6 @@ void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios)
 	plug->rq_count = 0;
 	plug->multiple_queues = false;
 	plug->has_elevator = false;
-	plug->nowait = false;
 	INIT_LIST_HEAD(&plug->cb_list);
 
 	/*

include/linux/blkdev.h

@@ -969,7 +969,6 @@ struct blk_plug {
 
 	bool multiple_queues;
 	bool has_elevator;
-	bool nowait;
 
 	struct list_head cb_list; /* md requires an unplug callback */
 };