code: def clean_stale_routes(self, peer, route_family=None):
          
  
          if route_family is not None:
              if route_family not in SUPPORTED_GLOBAL_RF:
                  raise ValueError('Given route family %s is not supported.' %
                                   route_family)
  
              tables = [self._global_tables.get(route_family)]
          else:
              tables = self._global_tables.values()
          for table in tables:
              table.cleanup_paths_for_peer(peer)
docs: Removes old routes from `peer` from `route_family` table.
  
          Routes/paths version number is compared with `peer`s current version
          number.