blk-mq: remove unused function hctx_allow_merges

since 9bddeb2a "blk-mq: make per-sw-queue bio merge as default .bio_merge"
there is no caller for this function.
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: Nweiping zhang <zhangweiping@didichuxing.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -1504,12 +1504,6 @@ static void blk_mq_bio_to_request(struct request *rq, struct bio *bio)
 	blk_account_io_start(rq, true);
 }
 
-static inline bool hctx_allow_merges(struct blk_mq_hw_ctx *hctx)
-{
-	return (hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
-		!blk_queue_nomerges(hctx->queue);
-}
-
 static inline void blk_mq_queue_io(struct blk_mq_hw_ctx *hctx,
 				   struct blk_mq_ctx *ctx,
 				   struct request *rq)