Remove Node polyfill needed for markdown-it / rich text components

[jattasNI]

🧹 Tech Debt

In #1335 we added a Node polyfill to our Rollup configuration because markdown-it relied on Node's punycode package but Nimble runs in the browser environment, not Node.

Since then, Node deprecated punycode and markdown-it added a dependency on an npm package that provides that support
markdown-it/markdown-it#967

This should allow us to remove the polyfill once we uptake that version of markdown-it and confirm that everything still works.
https://github.com/ni/nimble/blob/5181411fa3c370713b581c4640babd6b5b55bc6b/packages/nimble-components/rollup.config.js#L7C8-L7C21