docs: public Observable<Void> unregisterAsync(String resourceGroupName, String vaultName, String identityName) {
          return unregisterWithServiceResponseAsync(resourceGroupName, vaultName, identityName).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }