net: phy: Remove fallback to old C45 method

Now that all MDIO bus drivers which support C45 implement the c45
specific ops, remove the fallback to the old method.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>