Remove polyfill.io

[gotson]

polyfill.io has been compromised in 2024 and has been shutdown. The DITA example won't load anymore because of that.

https://blog.qualys.com/vulnerabilities-threat-research/2024/06/28/polyfill-io-supply-chain-attack

https://www.kaspersky.com/blog/polyfill-io-service-supply-chain-attacks/51635/