Sites Dashboard: Remove layout-related overrides from Dotcom and A4A

[okmttdhr]

Related to https://github.com/Automattic/dotcom-forge/issues/10139

Proposed Changes

This PR removes layout-related overrides from Dotcom and A4A.

For details of individual overrides, please refer to this post's pfYzsZ-15D-p2 "Style Overrides Removal" and "Remaining Style Overrides" sections.

Why are these changes being made?

https://github.com/Automattic/dotcom-forge/issues/10139

Testing Instructions

On both Calypso and A4A Live;

• Go to /sites
• Click any site
• Ensure nothing breaks

A4A Live

• Go to /overview
• Go to /marketplace/assign-license
• Ensure nothing breaks

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-128643

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-128643&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-128643&env=a8c-for-agencies

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[fushar]

Tested on wpcom and A4A; works well.

We might need to update other hosting pages like Themes, because now they have different border-bottom:

Sites	Themes

[andrii-lysenko]

Thank you for working on this.
This seems to work well and I haven't found any issues. The code looks good as well 👍