This reverts commit 120eb388.

Reason for revert: Maybe perturbed GC and caused optimization test to fail: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux64%20GC%20Stress%20-%20custom%20snapshot/33042?

Original change's description:
> Reland "[d8] Add d8 global variable"
> 
> This is a reland of 6798619a
> 
> Original change's description:
> > [d8] Add d8 global variable
> >
> > - Add a a "d8" global variable where d8 can provide helpers.
> >   This in in preparation of adding d8.log for testing our log parsers
> >   written in JavaScript.
> >
> > - Separate d8 helper creation into individual functions.
> >
> > Bug: v8:1064
> > Change-Id: I84e434452463afb93ae403f890d8841b20b00703
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2400990
> > Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> > Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#69801}
> 
> TBR=verwaest@chromium.org
> 
> Bug: v8:1064
> Change-Id: I656d550b5ec87dc52dbe6cbbdddf7151ce25031f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2403247
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Reviewed-by: Mythri Alle <mythria@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#69819}

TBR=cbruni@chromium.org,mythria@chromium.org,verwaest@chromium.org

Change-Id: If6df69e30b097c78eb0ff2676f5e5c219edfae5b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:1064
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2404323Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69823}