Revert "[iOS] Make Home Customization half sheet backgrounds clear on iOS 26"

This reverts commit a28a026111836b3056afae70e8e0b85e277b50b1.

Reason for revert: Builder failure on Libfuzzer Upload iOS Catalyst Debug
First failure (due to unused variable): https://ci.chromium.org/ui/p/chromium/builders/ci/Libfuzzer%20Upload%20iOS%20Catalyst%20Debug/111882/overview

Original change's description:
> [iOS] Make Home Customization half sheet backgrounds clear on iOS 26
>
> This change makes all Home Customization half-sheet backgrounds clear on
> iOS 26 to properly render the Liquid Glass effect. This follows Apple's
> best practices for Liquid Glass UI.
>
> Screenshots:
>
> Main page:
> https://drive.google.com/file/d/1wnbrsZcW3JDv0kYYEKdbkVicDSQIkPwr/view?usp=drive_link&resourcekey=0-UnpWY_-u183hl7tSrwCmWQ
>
> Magic Stack:
> https://drive.google.com/file/d/168U-oyAvjjp74j1BSx-bdKEbh-YUvBQZ/view?usp=drive_link&resourcekey=0-dzw5XRb0xpqnStnGHE0qpw
>
> Discover Feed:
> https://drive.google.com/file/d/19BSDbhl44SooSYprBgwjmqdNZD0KIxIY/view?usp=drive_link&resourcekey=0-JxcBZLeq4kHtPDSOi72WCA
>
> Enabled-by-default-reason: killswitch
> Fixed: 430257025,430532716,423695955
> Change-Id: I788597d80680786c74343499bae86246feef55f3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6872016
> Auto-Submit: Benjamin Williams <bwwilliams@google.com>
> Reviewed-by: Pier-Alexandre Bouchard <pabouchard@google.com>
> Commit-Queue: Benjamin Williams <bwwilliams@google.com>
> Reviewed-by: Gauthier Ambard <gambard@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1506660}

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I4bd08e8f53226d5d1d807e0177b5436c65c95c7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6885127
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Zonghan Xu <xzonghan@chromium.org>
Owners-Override: Zonghan Xu <xzonghan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1506698}