Remove all the duplicated ToGlibPtr impls for every single super-class
Remove all the duplicated ToGlibPtr impls for every single super-class

We can get those directly via the AsRef<T> impl on IsA<T> in all places
where it's needed, and this is the only reason why we currently have to
pass in the FFI types of all superclasses too.

rust-gnome/glib