Most addons live in the same network by default (matrix-addons) right now,
so this network would have usually been created by some other addon.
Howevre, if this is the only addon someone uses, it may have remained
uncreated causing a problem.
- forego removing Docker images - it's not effective anyway, because it
only removes the last version.. which is a drop in the bucket, usually
- do not reload systemd - it's none of our business. `--tags=start`,
etc., handle this
- combine all uninstall tasks under a single block, which only runs if
we detect traces (a leftover systemd .service file) of the component.
If no such .service is detected, we skip them all. This may lead to
incorect cleanup in rare cases, but is good enough for the most part.