Revert "Implement a method to trigger an automatic scroll"

This reverts commit 898215e2.

Reason for revert: The added browsertests are failing under ASAN/MSAN (https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests/45192/overview, https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20(1)/59613/overview, https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20ASan%20LSan%20Tests%20(1)/127047/overview). They were already disabled as flaky in crbug.com/358251460, but it seems that they are failing consistently, thus reverting this CL.

Original change's description:
> Implement a method to trigger an automatic scroll
>
> When the user scrolls to the end of the Reading Mode side panel, the main page
> will automatically scroll to the last line shown on the panel.
>
> Screenshot of where the document scrolls to:
> https://screenshot.googleplex.com/7x6CNiru7gCWtAp.png
>
> Bug: 353590969
> Change-Id: I05e0f64c67904e1188afa48d59773089f3618bd4
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5747514


> Reviewed-by: Abigail Klein <abigailbklein@google.com>
> Reviewed-by: Will Harris <wfh@chromium.org>
> Commit-Queue: Sophia Tran <sophiatran@google.com>
> Reviewed-by: Xiang Xiao <xiangxiao@google.com>
> Cr-Commit-Position: refs/heads/main@{#1338808}

Bug: 353590969
Change-Id: Id689a2f3c1f56f60363b31c0532fad5200860e4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5776885


Auto-Submit: Andrei Nedoluzhko <nedol@google.com>
Reviewed-by: Bastian Kersting <bkersting@google.com>
Owners-Override: Andrei Nedoluzhko <nedol@google.com>
Commit-Queue: Andrei Nedoluzhko <nedol@google.com>
Commit-Queue: Bastian Kersting <bkersting@google.com>
Cr-Commit-Position: refs/heads/main@{#1339634}