This reverts commit 347ba357.

Reason for revert: MSAN https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/39275/overview

Original change's description:
> [bigint] FFT-based multiplication
>
> The Schönhage-Strassen method for *very* large inputs.
>
> Bug: v8:11515
> Change-Id: Ie8613f54928c9d3f6ff24e3102bc809de9f4496e
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3000742
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Reviewed-by: Maya Lekova <mslekova@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#75659}

Bug: v8:11515
Change-Id: Ib0601e91bbd8ac5732b57730e3507eb0fa7e3947
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3015574
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@{#75660}