docs: def _deregister_config_file(self, key):
          """ Deregister a previously registered config file.  The caller should
          ensure that it was previously registered.
          """
          state = self.__load_state()
          if 'remove_configs' not in state:
              state['remove_configs'] = {}
          state['remove_configs'][key] = (state['config_files'].pop(key))
          self.__dump_state(state)