Having a duplicate prototype chain - once in FakeMetaObjects and once
in QmlObjectValues was unnecessary. Now FMOs don't contain references
which may allow other simplifications.
Previously they were leaked when a qmldump or the C++ exported QML
type list updated.
Just deleting the previous FakeMetaObjects is not an option, as they
might still be used in a QmlObjectValue owned by an Engine.
Reviewed-by: Erik Verbruggen
