--cleanup option no longer deletes projects

According to docs: "Using the --cleanup command line option, languages added to projects that no longer have matching files on the filesystem will be deleted.". However, the code would not only delete missing languages in projects (aka "translation projects"), but would also delete projects themselves. This has proven to be troublesome. For now, the --cleanup option will only affect translation projects. One can imagine a separate explicit "--delete-missing-projects" options to unregister projects as well.