*   The methods `Model.to_yaml()` and `keras.models.model_from_yaml` have
        been replaced to raise a `RuntimeError` as they can be abused to cause
        arbitrary code execution. It is recommended to use JSON serialization
        instead of YAML, or, a better alternative, serialize to H5.
    *   `LinearModel` and `WideDeepModel` are moved to the
        `tf.compat.v1.keras.models.` namespace