net: altera: tse: remove mac_an_restart() function

The mac_an_restart() method will only be called if the driver sets
legacy_pre_march2020, which the altera tse driver does not do.
Therefore, providing a stub is unnecessary.

Fixes: fef29982

 ("net: altera: tse: convert to phylink")
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>