Remove polyfill from mkdocs configuration

Author: yhteoh

mkdocs.yaml

@@ -119,7 +119,6 @@ markdown_extensions:
 
 extra_javascript:
   - javascripts/mathjax.js
-  - https://polyfill.io/v3/polyfill.min.js?features=es6
   - https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js
 
 extra_css: