Don't claim 3rd-party repos are part of the OS on Debian derivatives

This improves !474 (merged) on Debian and its derivatives (Ubuntu, PureOS, Pop_OS, ...) by only showing the distribution as the origin if it actually is the origin, and showing the raw repository name in any other case.

While the raw repo ID string is not pretty at all, and PackageKit still lacks an API to get that pretty name (which APT actually knows...) at least this change is more honest than claiming things are part of the OS that actually aren't.

(cherry picked from commit dc079431)