chore: remove polyfill.io from mkdocs

Author: xmatthias

mkdocs.yml

@@ -86,7 +86,6 @@ extra_css:
   - "stylesheets/ft.extra.css"
 extra_javascript:
   - javascripts/config.js
-  - https://polyfill.io/v3/polyfill.min.js?features=es6
   - https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js
 markdown_extensions:
   - attr_list