This now matters for CI, as the example is still built using fetchGit
instead of the github fetcher.
The example was doing double duty as an example and a stress-test,
enabling some problematic or interesting modules. That is no longer
necessary (once the branch with dynamically generated init.el with all
modules/flags enabled lands).
Although a completely empty DOOMDIR seems to work (at least for build
purposes), I doubt Doom actually supports this. And it requires some
extra checks on our side as well.
Just check in a trivial DOOMDIR and use that instead.
