We still had a few deprecated assignements of `bpy.props.xxx` to class
members in our API documentation and one of our py tests. Annotations
are to be used now.
Also remove the section about `register_module` utils, this has been
removed in 2.8.
Fix T71877: Python API overview sample code warning: class MyMaterialProps contains a property which should be an annotation!
Fix T71876: Python API overview references old bpy.utils.register_module function