Revert "Fix old html.css selectors for popover/dialog"

This reverts commit e4093d0bef4256e06d9b14ec5cc616a65042b11a.

Reason for revert: Causes https://crbug.com/393947100, which is worse (by far) than the bug this fixed.

Original change's description:
> Fix old html.css selectors for popover/dialog
>
> When the `overlay` property was added, these rules should have
> changed to simply look at whether the popover is a) a popover, and
> b) in the top layer. This CL fixes a bug where it was possible for
> a <dialog popover open> to be in the top layer, but not have the
> overlay:auto property, which caused painting issues.
>
> Fixed: 388538944
> Change-Id: I9665daef9f33ae61ea7bf82cb18429f14dab7d86
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6185344
> Reviewed-by: Joey Arhar <jarhar@chromium.org>
> Commit-Queue: Joey Arhar <jarhar@chromium.org>
> Auto-Submit: Mason Freed <masonf@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1409844}

Change-Id: Ic46f8fa18843caaa1bde154ce80c4aa16e11e2a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6226760
Auto-Submit: Mason Freed <masonf@chromium.org>
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1415097}