Audit list of classes in app/assets/stylesheets/highlight/hljs.scss

- These classes are used by an internal library and therefore aren't *directly*
  referenced. We need to keep them around.
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/164620#note_2097126033

app/assets/stylesheets/highlight/hljs.scss

+/**
+* These hljs css overwrite styling from 'highlight.js/lib/core'
+* Do not remove unless removing the library
+**/
+
 .code.highlight {
   .hljs-comment {
     color: var(--color-hljs-comment);