net: phylink: remove legacy mac_an_restart() method

The mac_an_restart() method is now completely unused, and has been
superseded by phylink_pcs support. Remove this method.

Since phylink_pcs_mac_an_restart() now only deals with the PCS, rename
the function to remove the _mac infix.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>