refactor junitTest cleanup

after executing the whole catroidTest package there were two testprojects in pocketcode folder.
calling TestUtils.deleteTestProjects deletes the default test project name, and can be used with additional parameter to delete a certain project (https://github.com/Catrobat/Catroid/blob/master/catroidTest/src/org/catrobat/catroid/test/utils/TestUtils.java#L195)