net: phy: stop exporting phy_driver_unregister

After 42e2a9e1 ("net: phy: dp83640: improve phydev and driver
removal handling") we can stop exporting also phy_driver_unregister().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/2bab950e-4b70-4030-b997-03f48379586f@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>