net: datalink: Remove unused declarations

These declarations is not used after ipx protocol removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230726144054.28780-1-yuehaibing@huawei.com


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