Use mozilla/fxc2.git for the fxc2 repository
As https://github.com/mozilla/fxc2/pull/1 is merged, we should replace the fxc2 repository with that instead of using a personal repository.
As https://github.com/mozilla/fxc2/pull/1 is merged, we should replace the fxc2 repository with that instead of using a personal repository.