Until now, we were leaving services "enabled"
(symlinks in /etc/systemd/system/multi-user.target.wants/).

We clean these up now. Broken symlinks may still exist in older
installations that enabled/disabled services. We're not taking care
to fix these up. It's just a cosmetic defect anyway.

When the playbook executes on a remote host (as it usually does),
we need to explicitly say `src` is a remote file and not relative
to the playbook.