This removes all the subdirectories in `config` on start.
From one version of GitLab to the next, the files in the `config`
directory changes. Since we're only overwriting the existing files
with ones from the repo, cruft sometimes gets left behind,
occationally causing issues.
Ideally, all configuration put in the `config` directory is declared
by NixOS options and we could just remove the whole directory on
start, but I'm not sure if that's the case. It would also require a
little bit of additional rework and testing. The subdirectories,
however, should seldom contain user configuration and the ones that
frequently does, `initializers`, is already removed on start.
2ec397ff9f