Drop support for Debian 10, Ubuntu 18, and FreeBSD 12

[wyardley]

Pull Request (PR) description

Drop metadata support for EOL OSes

• Drop support for Debian 10
• Drop support for Ubuntu 18.04
• Drop support for FreeBSD 12
• Remove some workarounds / hacks specific to older Debian-based systems.

~Note: we could / should theoretically drop support for CentOS / RHEL 7, but tests still don't function on 8 or 9.~ See #1027 for RHEL changes

This Pull Request (PR) fixes the following issue

[wyardley]

@bastelfreak going to handle CentOS separately, then can rebase this after.