virtiofs: delete unused parameter for virtio_fs_cleanup_vqs

fs parameter not used. So, it needs to be deleted.

Signed-off-by: Deming Wang <wangdeming@inspur.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>