net/mlx5e: Remove unused UDP GSO remaining counter

Remove tx_udp_seg_rem counter from ethtool output, as it is no longer
being updated in the driver's data flow.

Fixes: 3f44899e ("net/mlx5e: Use PARTIAL_GSO for UDP segmentation")
Signed-off-by: Mikhael Goikhman <migo@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>