net: phy: realtek: remove setting callback get_features and use phylib fallback

Now that phylib uses genphy_read_abilities() as fallback, we don't have
to set callback get_features any longer.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>