blkdev.h: remove unused codes blk_account_rq

Last users of blk_account_rq gone with patch commit a1ce35fa
("block: remove dead elevator code") and now it gets no caller, it can
be safely removed.
Signed-off-by: Lin Feng <linf@wangsu.com>
Link: https://lore.kernel.org/r/20210512100124.173769-1-linf@wangsu.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blkdev.h

@@ -677,11 +677,6 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
 extern void blk_set_pm_only(struct request_queue *q);
 extern void blk_clear_pm_only(struct request_queue *q);
 
-static inline bool blk_account_rq(struct request *rq)
-{
-	return (rq->rq_flags & RQF_STARTED) && !blk_rq_is_passthrough(rq);
-}
-
 #define list_entry_rq(ptr)	list_entry((ptr), struct request, queuelist)
 
 #define rq_data_dir(rq)		(op_is_write(req_op(rq)) ? WRITE : READ)