net: stmmac: Remove unused inline function stmmac_rx_threshold_count

There's no caller in-tree since
commit 2af6106a ("net: stmmac: Introducing support for Page Pool")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3543,15 +3543,6 @@ static void stmmac_rx_vlan(struct net_device *dev, struct sk_buff *skb)
 	}
 }
 
-
-static inline int stmmac_rx_threshold_count(struct stmmac_rx_queue *rx_q)
-{
-	if (rx_q->rx_zeroc_thresh < STMMAC_RX_THRESH)
-		return 0;
-
-	return 1;
-}
-
 /**
  * stmmac_rx_refill - refill used skb preallocated buffers
  * @priv: driver private structure