Update cleanup_build_jobs_leftovers for the vmdebootstrap → vmdb2 migration

https://gitlab.tails.boum.org/tails/puppet-tails/-/blob/master/files/jenkins/slaves/isobuilders/cleanup_build_jobs_leftovers has lots of stuff that's specific to vmdebootstrap. It's outdated since tails/tails#15349.

Note: For S11, this fits in:

• D.1 - Make Tails development process more efficient: Keeping deprecated code around created technical debt and impacts maintainability on the long run.

From FT's perspective

That’s tech debt. We understand there is no specific urgency in terms of Developer Experience. Doing this would benefit sysadmins more than Foundations Team.