Code review comment for lp://qastaging/~ubuntu-mate-dev/ubuntu-release-upgrader/ubuntu-mate-bionic-update

This defines all three of those metas as being the same now, which defeats the purpose of supporting more than one.

The point of KeyDependencies is to say "we have no meta installed, but we have this list of packages, so let's assume the user accidentally remove ubuntu-mate-desktop and needs it put back".