Reverted CQ changes to legacy right sidebar SCSS

What does this MR do and why?

This MR reverts change to container queries for right sidebar SCSS file to resolve the issue with right sidebar covering content. We don't need to migrate this file since it covers exclusively legacy UI; new UI is covered in https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/stylesheets/framework/application-chrome.scss#L515

References

https://gitlab.com/gitlab-org/gitlab/-/issues/567702#note_2784989654

Screenshots or screen recordings

Before	After
before	Screen_Recording_2025-09-30_at_15.03.48

How to set up and validate locally

1. Disable new UI
2. Visit any project issues pages like http://127.0.0.1:3000/flightjs/Flight/-/issues
3. Click New item button and create an incident.
4. Open an incident and try to collapse/expand right sidebar.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.