Docs: Review RC docs comments (#68714)
Closes:
https://linear.app/vercel/issue/DOC-3156/resolve-open-comments-in-rc-branch
Responded and closed all RC docs comments in preparation for [merging
the
docs](https://linear.app/vercel/issue/DOC-3155/close-rc-docs-pr-and-add-new-feature-tags).
With `experimental/canary` tags, we won't need to keep separate docs.
Changes:
- Fix code example
- Remove duplicate CRA upgrade guide
