code: def delete(self, image_file, delete_thumbnails=True):
          
          if delete_thumbnails:
              self.delete_thumbnails(image_file)
          self._delete(image_file.key)
docs: Deletes the reference to the ``image_file`` and deletes the references
          to thumbnails as well as thumbnail files if ``delete_thumbnails`` is
          `True``. Does not delete the ``image_file`` is self.