code: public Observable<Void> deleteAsync(String locationName, String longTermRetentionServerName, String longTermRetentionDatabaseName, String backupName) {
          return deleteWithServiceResponseAsync(locationName, longTermRetentionServerName, longTermRetentionDatabaseName, backupName).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Deletes a long term retention backup.
  
  @param locationName The location of the database
  @param longTermRetentionServerName the String value
  @param longTermRetentionDatabaseName the String value
  @param backupName The backup name.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request