block: remove QUEUE_FLAG_STACKABLE

We already have a queue_is_rq_based helper to check if a request_queue
is request based, so we can remove the flag for it.

Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/elevator.c b/block/elevator.c
index 153926a..7ae50eb 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1118,7 +1118,7 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
 	struct elevator_type *__e;
 	int len = 0;
 
-	if (!blk_queue_stackable(q))
+	if (!queue_is_rq_based(q))
 		return sprintf(name, "none\n");
 
 	if (!q->elevator)