message: Stop Model.save_weights from printing a deprication warning (TF format)
  Also has it save relative paths in the checkpoint proto, which removes a behavior difference between it and CheckpointManager.
diff: @@ -1382,9 +1382,10 @@ class Network(base_layer.Layer):
  % (optimizer,))
  self._checkpointable_saver.save(filepath, session=session)
  # Record this checkpoint so it's visible from tf.train.latest_checkpoint.
  - checkpoint_management.update_checkpoint_state(
  + checkpoint_management.update_checkpoint_state_internal(
  save_dir=os.path.dirname(filepath),
  model_checkpoint_path=filepath,
  + save_relative_paths=True,
  all_model_checkpoint_paths=[filepath])
  def load_weights(self, filepath, by_name=False):
  