net/mlx5: delete dead code in mlx5_esw_unlock()

Smatch complains about this function:

    drivers/net/ethernet/mellanox/mlx5/core/eswitch.c:2000 mlx5_esw_unlock()
    warn: inconsistent returns '&esw->mode_lock'.

Before commit ec2fa47d

 ("net/mlx5: Lag, use lag lock") there
used to be a matching mlx5_esw_lock() function and the lock and
unlock functions were symmetric.  But now we take the lock
unconditionally and must unlock unconditionally as well.

As near as I can tell this is dead code and can just be deleted.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>