How to permanently delete a MDS group and user data?

We played with temporary MDS groups and users for a while in MDS. When we deleted them, we found that even though we cannot see them on the User and Group Permissions page, we still see them in the underlaying tables such as mdm.tblUser, mdm.tblUserGroup, mdm.tblSecurityRole, mdm.tblSecurityAccessControl, etc. How do we get rid of them permanently from the database? Is it OK if we just do a delete from these tables using SQL?

Thanks In Advance