Deletes a device class subgroup. This subgroup is automatically created when a Device Update-enabled device is connected to the hub and reports its properties. Groups, subgroups, and deployments are not automatically cleaned up but are retained for history purposes. Users can call this method to delete a subgroup if they do not need to retain any of the history of the subgroup and no longer need it. If a device is ever connected again for this subgroup after the subgroup was deleted it will be automatically re-created but there will be no history.