Update dependency 'next-mdx-remote' (#1463)

### Description

The 'next-mdx-remote' dependency is affected by CVE-2026-0969 for
versions >= 4.3.0 < 6.0.0. PR updates next-mdx-remote to version 6.0.0
in solutions/blog example, and drops the dependency in
solutions/platforms-slate-supabase where it doesn't seem to be used.

### Demo URL

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### Type of Change

- [ ] New Example
- [x] Example updates (Bug fixes, new features, etc.)
- [ ] Other (changes to the codebase, but not to examples)

### New Example Checklist

- [ ] 🛫 `npm run new-example` was used to create the example
- [ ] 📚 The template wasn't used but I carefuly read the [Adding a new
example](https://github.com/vercel/examples#adding-a-new-example) steps
and implemented them in the example
- [ ] 📱 Is it responsive? Are mobile and tablets considered?

Author: jaclarke

solutions/blog/package.json

@@ -14,7 +14,7 @@
     "@vercel/speed-insights": "^1.0.9",
     "geist": "1.2.2",
     "next": "^16.0.10",
-    "next-mdx-remote": "^4.4.1",
+    "next-mdx-remote": "^6.0.0",
     "postcss": "^8.4.35",
     "react": "^19.2.1",
     "react-dom": "^19.2.1",