For a smooth upgrade from 10.04 to 10.10, I would like to remove all packages which are not in the default repositories (e.g. chromium PPA and third-party repositories). What is the easiest way (preferably CLI) to find and remove these packages?
Edit: this question is not restricted to PPA's, I have a x2go repository as well, so I'm looking for a generic command to remove packages belonging to a certain repository. For PPA's, the question How can PPAs be removed has great answers.