r8169: remove 810x_phy_power_up/down

The functionality of 810x_phy_power_up/down is covered by the default
clause in 8168_phy_power_up/down. Therefore we don't need these
functions.

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