Oh well, it's not that difficult. You just have to search the right tools (for package management, you can use apt-get, aptitude and the backend dpkg), then you ask the manual of those tools with the man command. You search things that interest you (in this case repairing a broken package or removing it) and you try it. If you're lucky, you'll get a helpful error message with a hint.
In this case, the first hint came from apt, about removing one specific package and the second hint from dpkg about some file that could not be removed. So creating an empty stub file worked.
Not everything must be done via the command line, but it's just easier to copy-paste an "rm" command than to describe what you have to remove and how.