Every plain `decnet deinit` ran userdel + groupdel unconditionally. In
dev the operator may pass `--user $USER --group $USER` to avoid file
ownership churn against a source checkout — at which point deinit
would cheerfully delete their own login account.
Move user/group removal behind --purge, matching the existing
behaviour for /var/lib/decnet + /var/log/decnet. Help text updated:
--purge now clearly advertises that it also wipes the service
user/group, with an explicit warning to only run it when `decnet init`
created the account in the first place.
Test updated: plain --deinit must NOT invoke userdel/groupdel;
--deinit --purge must.
anti
edc8297af3