docs: remove canary marker from next.config.ts (#71678)

## Summary
These notes are outdated.
it's available on v15 stable now.

### Improving Documentation

- [x] Run `pnpm prettier-fix` to fix formatting issues before opening
the PR.
- [x] Read the Docs Contribution Guide to ensure your contribution
follows the docs guidelines:
https://nextjs.org/docs/community/contribution-guide

x-ref: [Next.js 15 Blog](https://nextjs.org/blog/next-15)

Co-authored-by: JJ Kasper <jj@jjsweb.site>

docs/02-app/02-api-reference/05-next-config-js/index.mdx

@@ -99,8 +99,6 @@ module.exports = (phase, { defaultConfig }) => {
 
 ## TypeScript
 
-> This feature is available from Next.js canary.
-
 If you are using TypeScript in your project, you can use [`next.config.ts`](/docs/app/building-your-application/configuring/typescript#type-checking-nextconfigts) to use TypeScript in your configuration:
 
 ```ts filename="next.config.ts"