Ghost weapon worldmodel still visible when ghost should be invisible

[jason-e]

When a momtv ghost is set to be invisible it hides all entities tracked by the replay, but equipped weapons spawn their own client-side clone which is made visible in third person instead of the viewmodel version. The clone is not known by momtv so we need a way to make it invisible from momtv. We could also look into whether this cloning is even needed in our case (I have no idea) and if it isn't, we can just turn off cl_viewmodelsclonedasworld.