[Merge] ~juliank/software-properties:gtk-remove-cruft into software-properties:ubuntu/master

[Sebastien Bacher]

Review: Needs Fixing

Thanks. I think the first 3 changes make sense, those are deprecated/not working features. Could you back out the keyring message from that MP though? I think the current wording is not really clear and that we can probably do better there but that discussion shouldn't block the other changes from landing
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https://code.launchpad.net/~juliank/software-properties/+git/software-properties/+merge/477395
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