net/mlx5e: Remove unused mlx5e_dcbnl_build_rep_netdev function

Commit
7a9fb35e ("net/mlx5e: Do not reload ethernet ports when changing eswitch mode")
removed the usage of mlx5e_dcbnl_build_rep_netdev() from the driver,
delete the function.

Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>