def clean_app_id(app_id):
  """ Google App Engine uses a special prepended string to signal that it
  is an HRD application. AppScale does not use this string so we remove it.
  
  Args:
    app_id: A str, the application identifier.
  Returns:
    An application identifier without the HRD string.
  """
  if app_id.startswith("s~"):
    return app_id[2:]
  return app_id