net/mlx5: Remove unused mlx5_query_nic_vport_vlans

mlx5_query_nic_vport_vlans() is not used anymore. Hence remove it.
This patch doesn't change any functionality.

Signed-off-by: Bodong Wang <bodong@mellanox.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>