Delete a user group.
All the memberships and permissions associated with the user group are also deleted, but the users that are members of the group are not deleted.
To delete a user group, the user must be authorised to administer it, or they must be authorised to own users in it and the user group must be empty.
The user group can be passed by id or reference. If both are passed, id takes precedence.
101 - Not authorised
102 - not found
103 - parameter error