net/sched: Remove unused function qdisc_queue_drop_head()

It is not used since commit a09ceb0e ("sched: remove qdisc->drop")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -1047,12 +1047,6 @@ static inline unsigned int __qdisc_queue_drop_head(struct Qdisc *sch,
 	return 0;
 }
 
-static inline unsigned int qdisc_queue_drop_head(struct Qdisc *sch,
-						 struct sk_buff **to_free)
-{
-	return __qdisc_queue_drop_head(sch, &sch->q, to_free);
-}
-
 static inline struct sk_buff *qdisc_peek_head(struct Qdisc *sch)
 {
 	const struct qdisc_skb_head *qh = &sch->q;