net: ethernet: enetc: get rid of xdp_redirect_sg counter

Remove xdp_redirect_sg counter and the related ethtool entry since it is
no longer used.

Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>