Remove EE-specific comment markers from CE

What does this MR do?

EE MR, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5151

• Remove EE-specific comment markers from CE
• Add docs about not backporting the EE specific comment markers

Are there points in the code the reviewer needs to double check?

This will probably cause conflicts in the CE to EE merge. Should be simple to resolve because we just need to keep the EE-specific sections in EE.

Why was this MR needed?

Keeping the EE-specific comment markers in CE isn't necessary to reduce conflicts.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
  • Not a user-facing change
• Documentation created/updated
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #44752 (closed)