Remove the fake git driver

[markwalet]

Some of the unit tests depend on the FakeGitDriver, which is a helper class to make testing easier.

Right now this class is shipped in production code. And that is not intended.

With class mocking, it should be possible to remove the need of the fake driver completely. Tests should be adapted to use a mock. If it is necessary, we can also change the service provider loading structure. But this will result in a bigger update which we want to prevent.