[Merge] ~rbalint/ubuntu-release-upgrader:ubuntu/master into ubuntu-release-upgrader:ubuntu/master

[Julian Andres Klode]

@xnox This looks at the candidate's provides (or if you want, any version, candidate_only=False), hence the installed one not providing it is not a concern.

I don't want to argue about what the behavior should be wrt a package picking up a dependency, but this changes the behavior from what it used to be, and is for other packages in similar situations - they get removed.

Hence this changes more than necessary to resolve the bug, which might have broader implications as to how systems diverge from our expectations after an upgrade, which I don't want to get into days before the release.
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https://code.launchpad.net/~rbalint/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/382454
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