fix(oas31): use system.fn as source of truth for Model wrapper (#9153)

Refs #8577

src/core/plugins/oas31/wrap-components/model.jsx

@@ -4,10 +4,6 @@
 import React from "react"
 
 import { createOnlyOAS31ComponentWrapper } from "../fn"
-import {
-  makeIsExpandable,
-  getProperties,
-} from "../json-schema-2020-12-extensions/fn"
 
 const ModelWrapper = createOnlyOAS31ComponentWrapper(
   ({ getSystem, ...props }) => {
@@ -139,11 +135,8 @@ const ModelWrapper = createOnlyOAS31ComponentWrapper(
       },
       fn: {
         upperFirst: fn.upperFirst,
-        isExpandable: makeIsExpandable(
-          fn.jsonSchema202012.isExpandable,
-          getSystem
-        ),
-        getProperties,
+        isExpandable: fn.jsonSchema202012.isExpandable,
+        getProperties: fn.jsonSchema202012.getProperties,
       },
     })