Remove outdated templates (#1379)

### Description
Vercel Postgres and Vercel KV were deprecated (in favor of native
postgres and redis integrations on Vercel Marketplace). Removing some of
the example templates which used them.

I have already archived them on contentful.

Deleted templates:
- storage/kv-redis-waiting-room
- storage/postgres-nuxt
- storage/postgres-pgvector
- storage/postgres-prisma


### Demo URL
N/A

### 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?

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: bhrigu123