remove debconf

This is a first untested try at removing debconf. Going to wait for the Salsa CI pipelines to become operational again.

I chose to do this because this is largely indepdendent from the big groups-creation complex that is pending for experimental next week.

Following bugs may be affected;

• 541620 - decide whether to use ucf (plus local scaffolding) or dpkg conffile handling for adduser.conf
• 1012492
• 57280
• 398802
• 640651