fix: Simplify VersionWarning to show on all versioned subdomains (#11542)
## Summary
- Simplifies `VersionWarning` component to show a version notice on any
versioned subdomain (e.g., `v2-3-1.turborepo.dev`)
- Removes npm registry fetch and version comparison logic that was never
working as intended
## Context
The previous implementation tried to fetch the latest version from npm
and compare it to the subdomain version to determine if the docs were
"old." However, versioned subdomains don't serve archived documentation
- they all serve the same latest deployment. The subdomains exist
primarily for serving versioned `schema.json` files.
The new behavior simply shows an informational notice with the version
number and a link to the main docs site whenever a user is on any
versioned subdomain.