Deletes the specified example.

    Args:
      request: A request that should contain 'index'.

    Returns:
      An empty response.

def _delete_example(self, request):
    """Deletes the specified example.

    Args:
      request: A request that should contain 'index'.

    Returns:
      An empty response.
    """
    index = int(request.args.get('index'))
    if index >= len(self.examples):
      return http_util.Respond(request, {'error': 'invalid index provided'},
                               'application/json', code=400)
    del self.examples[index]
    self.updated_example_indices = set([
        i if i < index else i - 1 for i in self.updated_example_indices])
    self.generate_sprite([ex.SerializeToString() for ex in self.examples])
    return http_util.Respond(request, {}, 'application/json')