Remove unused methods and their tests

Pretty much self explaining. 

But one thing should be mentioned, for clarity: `getProjectFiles()` which was unused but had tests has been removed, but the test has been adapted to test `getProjectNames()` which *is* used but had no tests.

[Testrun](https://jenkins.catrob.at/view/All-Categories/view/Catroid/job/Catroid-Multi-Job-Custom-Branch/688/)