Remove jQuery class from the `repo-issue.js` file (#30192)

Remove jQuery class from the `repo-issue.js` file (#30192)

Switched from jQuery class functions to plain JavaScript `classList`.

Tested the following functionalities and they work as before:
- delete issue comment
- cancel code comment
- update (merge or rebase) pull request
- re-request review
- reply to code comment
- show/hide outdated comments
- add code comment
- edit issue title

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Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: silverwind <me@silverwind.io>