This was a bad design choice since it doesn't allow us to easily manage
the intended plugin version and therefore keep them up to date.
As a short-term mechanism, we change the used variables to have the
_OVERRIDE suffix and default in dd-ctl to the actual URLs, while also
removing them from dd.conf.sample.
This solves the issue in both current and future installations; in a
near future we want to have these dependencies in a .tsv file where they
can easily be managed.
Evilham