* Replace `tf.keras.mixed_precision.experimental.get_layer_policy(layer)` with `layer.dtype_policy`.
* `tf.mixed_precision.experimental.LossScale` and its subclasses have been removed from the TF2 namespace. This symbols were very rarely used and were only useful in TF2 for use in the now-removed `tf.keras.mixed_precision.experimental` API. The symbols are still available under `tf.compat.v1.mixed_precision`.