code: def _remove_redundancy_router_interfaces(self, context, router_id,
                                               old_port):
          
          ha_settings = self._get_ha_settings_by_router_id(context, router_id)
          if ha_settings is None or old_port is None:
              return
          e_context = context.elevated()
          rr_ids = self._get_redundancy_router_ids(e_context, router_id)
          port_info_list = self._core_plugin.get_ports(
              e_context, filters={'device_id': rr_ids,
                                  'network_id': [old_port['network_id']]},
              fields=['device_id', 'fixed_ips', 'id'])
          subnet_id = old_port['fixed_ips'][0]['subnet_id']
          for port_info in port_info_list:
              if port_info['fixed_ips'][0]['subnet_id'] == subnet_id:
                  interface_info = {'port_id': port_info['id']}
                  self.remove_router_interface(e_context, port_info['device_id'],
                                               interface_info)
          self._delete_ha_group(e_context, old_port['id'])
docs: To be called in delete_router_interface() BEFORE interface has been
          removed from router in DB.