block: cleanup REQ_SOFTBARRIER usages

blk_insert_request() doesn't need to worry about REQ_SOFTBARRIER.
Don't set it.  Combined with recent ide updates, REQ_SOFTBARRIER is
now only used in elevator proper and for discard requests.

[ Impact: cleanup ]
Signed-off-by: Tejun Heo <tj@kernel.org>

block/blk-core.c

@@ -946,7 +946,6 @@ void blk_insert_request(struct request_queue *q, struct request *rq,
 	 * barrier
 	 */
 	rq->cmd_type = REQ_TYPE_SPECIAL;
-	rq->cmd_flags |= REQ_SOFTBARRIER;
 
 	rq->special = data;