net: phylink: remove phylink_set_10g_modes()

phylink_set_10g_modes() is no longer used with the conversion of
drivers to phylink_generic_validate(), so we can remove it.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>