code: def remove_ref(self, ref):
          
          self.session.remove_ref(self, ref)
          return self.fetch()
docs: Remove reference from self to ref
  
          >>> iip = Resource('instance-ip',
                             uuid='30213cf9-4b03-4afc-b8f9-c9971a216978',
                             fetch=True)
          >>> for vmi in iip['virtual_machine_interface_refs']:
                  iip.remove_ref(vmi)
          >>> iip['virtual_machine_interface_refs']
          KeyError: u'virtual_machine_interface_refs'
  
          :param ref: reference to remove
          :type ref: Resource
  
          :rtype: Resource