This reverts commit c4b44d5d.

Reason for revert: UBSan failures (https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20UBSan/15621/overview)

Original change's description:
> [bigint] Begin src/bigint refactoring
>
> This patch moves a first function, Compare, from src/objects/bigint.cc
> to src/bigint/, to blaze the trail. More to follow!
>
> Bug: v8:11515
> Change-Id: Id7fa0b40ea852dbed1360f7ab439cb32d0c15762
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2737295
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73511}

Bug: v8:11515
Change-Id: I98f3e385c785297b1b71de07fc4835da2bbe816c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2773048
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#73515}