Please don't try to delete MASS Collaboration project in Work-bench.
If you wanna out from collaboration or any sharing through work-bench than please tell the Author to remove you.
He will remove you securely without any trouble.
If you delete the collaboration project means, its too bad for all project's owner to do again so hard work to make it..!!
Ask to Author, to remove you from workbench collaboration project. If you are not interested..!!