Remove the usage of cdn.polyfill.io in the Styleguide Reader

[gido]

polyfill.io, a popular JavaScript library service, can no longer be trusted and should be removed from websites.

It's currently used in the Styleguide Reader (https://epfl-si.github.io/elements/#/).

I propose to completely remove the third party library as every recent (and not so recent) browser natively support the feature requested.

More informations:

• https://sansec.io/research/polyfill-supply-chain-attack
• Drupal PSA: https://www.drupal.org/psa-2024-06-26

[williambelle]

@gido Thank you