docs: def unregister_callback(self, callback_url, **kwargs):
          """
          Unregister a callback.
  
          Unregisters a callback URL that was previously white-listed with a **Register a
          callback** request for use with the asynchronous interface. Once unregistered, the
          URL can no longer be used with asynchronous recognition requests.
          **See also:** [Unregistering a callback
          URL](https://cloud.ibm.com/docs/services/speech-to-text/async.html#unregister).
  
          :param str callback_url: The callback URL that is to be unregistered.
          :param dict headers: A `dict` containing the request headers
          :return: A `DetailedResponse` containing the result, headers and HTTP status code.
          :rtype: DetailedResponse
          """
  
          if callback_url is None:
              raise ValueError('callback_url must be provided')
  
          headers = {}
          if 'headers' in kwargs:
              headers.update(kwargs.get('headers'))
          sdk_headers = get_sdk_headers('speech_to_text', 'V1',
                                        'unregister_callback')
          headers.update(sdk_headers)
  
          params = {'callback_url': callback_url}
  
          url = '/v1/unregister_callback'
          response = self.request(
              method='POST',
              url=url,
              headers=headers,
              params=params,
              accept_json=False)
          return response