net/mlx5e: remove unused list in arfs

This is never used, and probably something that was intended to be used
before per-protocol hash tables were chosen instead.

Signed-off-by: Anisse Astier <anisse@astier.eu>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>