[Make] - don't install .git directories

When i fixed the submodules on jenkins we realised that on some strange situations the android slaves bailed out because of the submodule.

I investigated a bit further and the problem was that whenever the depends were changed (e.x. when switching between Gotham and master builds) jenkins issued a git clean -xfd. This failed because there was a .git folder in the prefix (the one from skin.touched submodule ;) ) and git clean tried to find the parent of that submodule (there is no parent in the prefix of course).

I remember also seeing .git folders in our ios deb files. I guess its the same reason. Basically this is some remnant from svn times i think? We should never install .git folders.

@wsnipex @koying this should be sane right?