Draft: Simplify/Update validation instructions for CPAchecker

Created by: MartinSpiessl

For people who are users of the GraphML format the instructions on how to configure CPAchecker to do a witness validation with a non-standard analysis should not be listed here. If at all, they should be listed in the CPAchecker documentation. The plan is to eventually move these instructions to: https://sosy-lab.gitlab.io/research/tutorials/CPAchecker/Witnesses.html along with some additional information on how to do the same with correctness witnesses.

I still need to look at the other calls of CPAchecker and will probably also simplify those commands (no need to pass many of the configuration options on command line, we have much easier ways to do this nowadays).