r8169: remove rtl8168c_4_hw_phy_config

rtl8168c_4_hw_phy_config() duplicates rtl8168c_3_hw_phy_config(),
so we can remove the function.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>