[post-trixie]

We already have deluser --system refusing to delete a non-system
account.

Otoh, shuold deluser (without --system) delete a system account? The
manpage says that deluser without --system will delete a non-system
account, should we enforce that?

This has surfaced when writing symmetric test cases.

Greetings
Marc

Enforcing this will render some packages buggy, namly those that create
their account with adduser --system but delete it without the --system
option. A superficial search on codesearch.debian.net turned up at least
those:

arpalert
beanstalkd
clamsmtp
davfs
dbeacon
debian-edu-fai
dmarcts-report-parser
e2guardian
ejabberd
email-reminder
gitlab-ci-multi-runner
gitolite
gitolite3
ident2
identd
mdns-reflector
milter-greylist
planetfilter
policyd-weight
postfwd
prelude-correlator
prelude-manager
sslh
syncache
tuptime
vdradmin

So we'd need to do a small mass bug filing on those before we actually
implement this change.

Greetings
Marc