[StartRefactor] Clean up refactor code in LayoutManager.

Remove overviewLayout in LayoutManagerChrome and its tests.

Bug: 40221888
Change-Id: Icb594c35be9ecee1b4ffcda5938109c5137b670c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5335422


Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Xinyi Ji <xinyiji@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1267427}