ANDROID: Remove Unpacker and plugin related things

Also remove the splash screen that happend during unpacking.

The unpacker is needed for loading plugins, which we don't do.


Side effect: This causes ResidualVM to start to a black screen. It is the same black screen that happened after the unpacker was done. I think we should try to just lower the amount of time the screen is black for, rather than have a splash of some kind, but it might worsen the user experience to not have some kind of splash. I'm not experience enough with android development to have a splash though. I could leave in the layout files for now, but if someone does add a splash I think the current spash won't really work well for that.