This reverts commit 81dd3f42.

Reason for revert: Does not compile on MSVC: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Win64%20-%20msvc/18017/overview

Original change's description:
> Reland "[bigint] Karatsuba multiplication"
>
> This is a reland of 59eff3bf
>
> Original change's description:
> > [bigint] Karatsuba multiplication
> >
> > The Karatsuba algorithm is used for BigInts with 34 or more internal
> > digits, and thanks to better asymptotic complexity provides greater
> > speedups the bigger the inputs.
> >
> > Bug: v8:11515
> > Change-Id: I5ab0e318173ea4a02ced3f156d3c17e0259c5036
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2782283
> > Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> > Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> > Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#74916}
>
> Bug: v8:11515
> Change-Id: I5ece2ff29ef11ea304980c053887d9746cfc80bc
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2933497
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74922}

Bug: v8:11515
Change-Id: Ie4a80256174fc8d9f714c01f012ac2dc6247a220
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2933665
Auto-Submit: Clemens Backes <clemensb@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@{#74926}