examples(with-mdx): update to MDX 3

The example was 2 major versions behind.

The `@mdx-js/react` dependency was removed, as it doesn’t work with the
app directory. Users should use `mdx-components.tsx` instead.

Refs #59693

examples/with-mdx/package.json

@@ -6,8 +6,7 @@
     "start": "next start"
   },
   "dependencies": {
-    "@mdx-js/loader": "^1.5.1",
-    "@mdx-js/react": "^1.6.18",
+    "@mdx-js/loader": "^3.0.1",
     "@next/mdx": "^9.1.1",
     "next": "latest",
     "react": "^18.2.0",