vyos.ethtool: T3163: drop obsoleted is_fixed_lro() method
vyos.ethtool: T3163: drop obsoleted is_fixed_lro() method

Commit d22f97af ("vyos.ethtool: T3163: rename unused methods for offload
validation") reworked the entire class on how data should be presented to the
user, but forgot to drop the is_fixed_lro() method.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x