message: Convert unused headings to comments.
diff: See @{$python/contrib.rnn} guide.
  -# From core
  +<!--From core-->
  @@RNNCell
  @@BasicRNNCell
  @@BasicLSTMCell
  @@ -28,12 +28,12 @@ See @{$python/contrib.rnn} guide.
  @@DeviceWrapper
  @@ResidualWrapper
  -# Used to be in core, but kept in contrib.
  +<!--Used to be in core, but kept in contrib.-->
  @@EmbeddingWrapper
  @@InputProjectionWrapper
  @@OutputProjectionWrapper
  -# Created in contrib, eventual plans to move to core.
  +<!--Created in contrib, eventual plans to move to core.-->
  @@LayerNormBasicLSTMCell
  @@LSTMBlockWrapper
  @@LSTMBlockCell
  @@ -57,11 +57,11 @@ See @{$python/contrib.rnn} guide.
  @@HighwayWrapper
  @@GLSTMCell
  -# RNNCell wrappers
  +<!--RNNCell wrappers-->
  @@AttentionCellWrapper
  @@CompiledWrapper
  -# RNN functions
  +<!--RNN functions-->
  @@static_rnn
  @@static_state_saving_rnn
  @@static_bidirectional_rnn
  