message: Update CHANGES.md to mention removal of material assets.
diff: # Change Log
  +### ? - ?
  +
  +##### Breaking Changes :mega:
  +
  +- Removed the following material assets that were accidentally included in the plugin in v1.13.0: `MetadataStyling/Layers/NYCBuildings_ByHeight_ML`, `MetadataStyling/Layers/NYCBuildings_ByYear_ML`, `MetadataStyling/NYCBuildings_ByHeight_M`, and `MetadataStyling/NYCBuildings_ByYear_M`. These assets can still be found in the [Cesium for Unreal Samples](https://github.com/CesiumGS/cesium-unreal-samples) project.
  +
  ### v1.13.0 - 2022-05-02
  ##### Breaking Changes :mega:
  