blk-mq: remove stale comment for blk_mq_complete_request()

It works for both IPI and local completions as of commit
95f09684.
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/blk-mq.h

@@ -172,11 +172,6 @@ void blk_mq_end_io(struct request *rq, int error);
 void __blk_mq_end_io(struct request *rq, int error);
 
 void blk_mq_requeue_request(struct request *rq);
-
-/*
- * Complete request through potential IPI for right placement. Driver must
- * have defined a mq_ops->complete() hook for this.
- */
 void blk_mq_complete_request(struct request *rq);
 
 void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx);