[SECURITY] Bug 219690: When deleting products and the 'usebuggroups' parameter is...

[SECURITY] Bug 219690: When deleting products and the 'usebuggroups' parameter is on, the privilege which allows someone to add people to the group which is being deleted does not get removed, allowing people with that privilege to get that privilege for the next group that is created which reuses that group ID.  Note that this only allows someone who had been granted privileges in the past to retain them.
Patch by Stefan Mayr <S.Mayr2@cadenas.de>
r= justdave, joel  a= justdave