code: def remove_extension(module, name, code):
      
      key = (module, name)
      if (_extension_registry.get(key) != code or
          _inverted_registry.get(code) != key):
          raise ValueError("key %s is not registered with code %s" %
                           (key, code))
      del _extension_registry[key]
      del _inverted_registry[code]
      if code in _extension_cache:
          del _extension_cache[code]
docs: Unregister an extension code.  For testing only.