Remove compatibility workaround for Mathjax and Kramdown

The underlying issue got fixed as described in https://github.com/gettalong/kramdown/issues/651
8 jobs for 57-revisit-mathjax-3-and-kramdown-compatibility in 7 minutes and 48 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Build
passed build:latest #167891

00:03:42

passed build:production #167894

00:04:06

passed build:production:review-apps #167893

00:04:05

passed build:production:subpath #167892

00:04:31

 
  Test
passed test:htmlproofer #167895

00:01:06

passed test:htmlproofer:subpath #167896

00:03:13

 
  Review
passed review #167897
review-apps

00:00:06

passed stop_review #167898
review-apps manual

00:00:01