vdpa/mlx5: Remove flow counter from steering

The flow counter has been introduced in early versions of the driver to
aid in debugging. It is no longer needed and can harm performance.

Remove it.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Message-Id: <20220411122942.225717-2-elic@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>