code: function clearOfflineLogin(credentials, serverOptions) {
      // simultaneous logins using different credentials is not realized so far,
      // so that the credentials parameter is irrelevant, but provided for the
      // sake of completeness...
      try {
          localStorage().removeItem(computeLocalStorageKey(serverOptions));
          return Q.resolve(undefined);
      }
      catch (error) {
          return Q.reject(error);
      }
  }
docs: deletes stored login response of some server.
  
  @param credentials allowing to differentiate when multiple logins are used simultaneously, may
  be null to forget just anything.
  @param serverOptions identifying the server.
  @return {Promise<void>} indicating success or failure.
  
  @internal Not part of public API, for library use only.