code: public Observable<OperationStatus> deleteUnlabelledUtteranceAsync(UUID appId, String versionId, String utterance) {
          return deleteUnlabelledUtteranceWithServiceResponseAsync(appId, versionId, utterance).map(new Func1<ServiceResponse<OperationStatus>, OperationStatus>() {
              @Override
              public OperationStatus call(ServiceResponse<OperationStatus> response) {
                  return response.body();
              }
          });
      }
docs: Deleted an unlabelled utterance.
  
  @param appId The application ID.
  @param versionId The version ID.
  @param utterance The utterance text to delete.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the OperationStatus object