block: remove the rq_alloc_data request_queue field

Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blkdev.h

@@ -567,7 +567,6 @@ struct request_queue {
 	bool			mq_sysfs_init_done;
 
 	size_t			cmd_size;
-	void			*rq_alloc_data;
 
 	struct work_struct	release_work;