avm2: Replace two more uses of `instance_of` with `instance_class`

core/src/avm2/globals/avmplus.rs

@@ -275,7 +275,7 @@ fn describe_internal_body<'gc>(
     let super_vtable = if use_instance_traits {
         class_obj.superclass_object().map(|c| c.instance_vtable())
     } else {
-        class_obj.instance_of().map(|c| c.instance_vtable())
+        class_obj.instance_class().map(|c| c.instance_vtable())
     };
 
     if flags.contains(DescribeTypeFlags::INCLUDE_INTERFACES) && use_instance_traits {

core/src/avm2/object/class_object.rs

@@ -224,7 +224,7 @@ impl<'gc> ClassObject<'gc> {
         activation: &mut Activation<'_, 'gc>,
     ) -> Result<(), Error<'gc>> {
         let class = self.inner_class_definition();
-        self.instance_of().ok_or(
+        self.instance_class().ok_or(
             "Cannot finish initialization of core class without it being linked to a type!",
         )?;