rt2x00: remove redundant functions rt2x00mac_sta_{add/remove}

Only rt2800 subdriver of rt2x00 implement sta_add() and sta_remove(),
rt2x00mac_sta_add and rt2x00mac_sta_remove has no callers after
commit 9c87758cf089 ("rt2x00: call sta_add/remove directly in rt2800").
So can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ralink/rt2x00/rt2x00mac.c

@@ -527,24 +527,6 @@ int rt2x00mac_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 EXPORT_SYMBOL_GPL(rt2x00mac_set_key);
 #endif /* CONFIG_RT2X00_LIB_CRYPTO */
 
-int rt2x00mac_sta_add(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
-		      struct ieee80211_sta *sta)
-{
-	struct rt2x00_dev *rt2x00dev = hw->priv;
-
-	return rt2x00dev->ops->lib->sta_add(rt2x00dev, vif, sta);
-}
-EXPORT_SYMBOL_GPL(rt2x00mac_sta_add);
-
-int rt2x00mac_sta_remove(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
-			 struct ieee80211_sta *sta)
-{
-	struct rt2x00_dev *rt2x00dev = hw->priv;
-
-	return rt2x00dev->ops->lib->sta_remove(rt2x00dev, sta);
-}
-EXPORT_SYMBOL_GPL(rt2x00mac_sta_remove);
-
 void rt2x00mac_sw_scan_start(struct ieee80211_hw *hw,
 			     struct ieee80211_vif *vif,
 			     const u8 *mac_addr)