Context:

While looking at #60618, I found out the TypeScript 7 upgrade only
breaks the `typescript-language-server` adapter, not the default vtsls
adapter.

After digging in, it turns out the initial vtsls implementation in
#12606 followed the same two-package installation pattern as the
`typescript-language-server` adapter: it installed both
`@vtsls/language-server` and the latest `typescript`. However, vtsls
already bundles a compatible TypeScript version via
`@vtsls/language-service` and uses it whenever a workspace SDK is
unavailable.

I also cross-checked an intermediate vtsls upgrade issue, #18349, where
we used the installed TypeScript version to decide whether both packages
needed updating, so a new vtsls release could go uninstalled when
TypeScript hadn't changed. #20197 fixed that by checking both packages
independently, but kept the unnecessary standalone TypeScript
installation.

Changes: 

This PR removes that redundant installation and version tracking from
the vtsls adapter. Zed now tracks only `@vtsls/language-server` and
relies on its declared TypeScript dependency. Workspace TypeScript and
Yarn SDK detection remain unchanged, so vtsls still uses a workspace SDK
when one is available and otherwise falls back to its bundled version.

As for the consequence of this change:
1. New users are not affected since npm installs vtsls's own pinned
TypeScript dependency anyway.
2. For existing users, the previously installed standalone `typescript`
was never resolvable by vtsls (its pinned version gets installed nested
when the versions conflict), so leaving it there is harmless.

To verify the standalone copy was really unused, I nuked the vtsls dir
and ran main (without this fix), which installed both the top-level
`typescript@7.0.2` and vtsls's own pinned `typescript@5.9.3` nested
under `@vtsls/language-service`. Node's module resolution shows vtsls
can only ever see the nested copy as well as the LSP logs from the
running server shows, all lib definition locations point at the nested
copy:

```
"uri": "file:///.../vtsls/node_modules/@vtsls/language-service/node_modules/typescript/lib/lib.es5.d.ts"
```

I also tested this branch with a fresh install TypeScript files work the
same as before.

Release Notes:

- N/A