Disabled `StarFold` tests

[ibbem]

Currently, the StarFold tests are disabled because DiffTree.toTextDiff has been removed (see #70). As StarFold is currently unused we have the choice of either fixing the tests or removing StarFold.

[pmbittner]

There is no real use case for StarFold anymore. We used it to try out an idea but it did not work as intended in the end. So we should delete the StartFold class and the corresponding test cases and data (if there is any).