ethtool: remove ethtool_eee_use_linkmodes

After 292fac46

 ("net: ethtool: eee: Remove legacy _u32 from keee")
this function has no user any longer.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/b4ff9b51-092b-4d44-bfce-c95342a05b51@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>