Search through all wikis and mark pages that should be removes with the keyword "deprecated".
The main criteria for removing a page would be that technical information is no longer valid for the 2 latest releases.
Another criteria would be that it is development documentation that deals with already implemented features.
The next criteria would be that the documentation is duplicating other parts of the documentation (not in different versions of the 1.x documentation) or in conflict with other parts of the docs.
The found pages should be posted to comments of this ticket too.