blk-mq-sched: remove unused 'can_block' arg from blk_mq_sched_insert_request

After commit:

923218f6166a ("blk-mq: don't allocate driver tag upfront for flush rq")

we no longer use the 'can_block' argument in
blk_mq_sched_insert_request(). Kill it.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Added actual commit message as to why it's being removed.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 2ff7cf0..55c0a74 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -427,7 +427,7 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
 }
 
 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
-				 bool run_queue, bool async, bool can_block)
+				 bool run_queue, bool async)
 {
 	struct request_queue *q = rq->q;
 	struct elevator_queue *e = q->elevator;