[packagekit] New method: RepoRemove()

[Richard Hughes]

Hi all,

I've pushed a new transaction method called RepoRemove() to master.
This is a method that when implemented removed a repo, *and* any
packages previously installed from that repo. This ensures two things:

* There are no errors when depsolving in the future
* Apps that are not going to have security updates are not left on the
users system

I've been asked to do this for GNOME software, to show (and optionally
remove) add-on repos like google-chrome and bluejeans. If you've got
any questions, please ask and I can explain how I've done this in the
hawkey backend.

Richard.