Revert "Reenable scroll-animations/element-based-offset tests"

This reverts commit bc2f9ba029056f669cfd0a71fe4b2bad6b58b494.

Reason for revert: The test is still flaky.

Original change's description:
> Reenable scroll-animations/element-based-offset tests
>
> The underlying source of the test flakes was likely addressed in
> recent changes to the handling of play and pause for scroll-linked
> animations.
>
> https://chromium-review.googlesource.com/c/chromium/src/+/2386339
>
> This patch also contains a cleanup to remove the unnecessarily
> convoluted way of hiding the scrollbar for the clamped offset test.
>
> Tested with 1000+ retries of the two tests in a virtual threaded
> environment.
>
> Bug: 1080609
> Change-Id: If9097b0a2017a9c87a359b61ba93f35bae56b512
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2475935
> Reviewed-by: Xida Chen <xidachen@chromium.org>
> Commit-Queue: Kevin Ellis <kevers@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#817568}

TBR=kevers@chromium.org,xidachen@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1080609
Change-Id: Ic31eede5561182d78e7bf805cd1f112edfd5379c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2483585
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818355}