def delete(self, image_file, delete_thumbnails=True):
        """
        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.
        """
        if delete_thumbnails:
            self.delete_thumbnails(image_file)
        self._delete(image_file.key)
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.