Remove stylesheet link to a deleted error tracking page bundle

What does this MR do and why?

Remove the call to add_page_specific_style 'page_bundles/error_tracking_index' from the error tracking index view.

Commit a30b6fab deleted the stylesheet app/assets/stylesheets/page_bundles/error_tracking_index.scss on 2024-12-05 but left this call in the view.

Each page load now requests a deleted stylesheet, causing the browser to log "Refused to apply style ... because its MIME type ('text/html') is not a supported stylesheet MIME type".

Nothing uses the deleted styles any more (the Vue app was moved to GlTable and utility classes in the same commit), so the fix is to remove the call.

References

• Part of section D of #628901
• Console check and baseline allowlist MR !255207 (closed)
• Reveal pipeline job showing the error https://gitlab.com/gitlab-org/gitlab/-/jobs/16462296254
• Commit that deleted the stylesheet a30b6fab

Screenshots or screen recordings

Not applicable. No visible UI change. The stylesheet had no effect since 2024.

How to set up and validate locally

1. Check out the branch.
2. Visit a project's Monitor > Error Tracking page with the browser console open.
3. Confirm there is no "Refused to apply style" message.

MR acceptance checklist

This MR was evaluated against the acceptance checklist at https://docs.gitlab.com/development/code_review/#acceptance-checklist.