block: remove the blk_flush_integrity call in blk_integrity_unregister

Now that there are no indirect calls for PI processing there is no
way to dereference a NULL pointer here.  Additionally drivers now always
freeze the queue (or in case of stacking drivers use their internal
equivalent) around changing the integrity profile.

This is effectively a revert of commit 3df49967 ("block: flush the
integrity workqueue in blk_integrity_unregister").
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20240613084839.1044015-7-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-integrity.c

@@ -401,8 +401,6 @@ void blk_integrity_unregister(struct gendisk *disk)
 	if (!bi->tuple_size)
 		return;
 
-	/* ensure all bios are off the integrity workqueue */
-	blk_flush_integrity();
 	blk_queue_flag_clear(QUEUE_FLAG_STABLE_WRITES, disk->queue);
 	memset(bi, 0, sizeof(*bi));
 }