block: get rid of unused blkdev_free_rq() define

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-core.c b/block/blk-core.c
index 5e14b3f..7b63c9b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -732,7 +732,6 @@
 		__freed_request(q, rw ^ 1);
 }
 
-#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
 /*
  * Get a free request, queue_lock must be held.
  * Returns NULL on failure, with queue_lock held.