code: public Observable<Void> deleteFaceAsync(String personGroupId, UUID personId, UUID persistedFaceId) {
          return deleteFaceWithServiceResponseAsync(personGroupId, personId, persistedFaceId).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Delete a face from a person. Relative image for the persisted face will also be deleted.
  
  @param personGroupId Id referencing a particular person group.
  @param personId Id referencing a particular person.
  @param persistedFaceId Id referencing a particular persistedFaceId of an existing face.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponse} object if successful.