docs: remove eval polyfill.io

[kricsleo]

polyfill.io has been proven to be evil as it recently started implanting malicious scripts to jump to gambling sites.

https://blog.cloudflare.com/automatically-replacing-polyfill-io-links-with-cloudflares-mirror-for-a-safer-internet

[CLAassistant]

All committers have signed the CLA.

[kricsleo]

Similar to https://github.com/javascript-tutorial/en.javascript.info/pull/3711, but only removes the polyfill.io

[smith558]

Thank you for your contribution! 🙂