This reverts commit 2221f090.

Reason for revert: fix in patchset 2

Original change's description:
> Revert "cppgc: Provide jobs support through DefaultPlatform and TestPlatform"
>
> This reverts commit 22c0fc8f.
>
> Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20gcc/8712?
>
> Original change's description:
> > cppgc: Provide jobs support through DefaultPlatform and TestPlatform
> >
> > This CL extends cppgc::DefaultPlatform and TestPlatform to emulate
> > jobs using std::thread and v8::base::Thread respectively.
> > Jobs using these platform do not yield unless the job as been
> > cancelled. Additionally, the job priority is ignored.
> >
> > Bug: chromium:1056170
> > Change-Id: I72db1eef410d2be3d3e5ea7d4ece9e5584a451f2
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2416378
> > Commit-Queue: Omer Katz <omerkatz@chromium.org>
> > Reviewed-by: Anton Bikineev <bikineev@chromium.org>
> > Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#70139}
>
> TBR=mlippautz@chromium.org,bikineev@chromium.org,omerkatz@chromium.org
>
> Change-Id: Ic29235e3ab78a1b515a5b14b808e116a1ccffc0f
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: chromium:1056170
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2432087
> Reviewed-by: Francis McCabe <fgm@chromium.org>
> Commit-Queue: Francis McCabe <fgm@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#70142}

# Not skipping CQ checks because this is a reland.

Bug: chromium:1056170
Change-Id: Iaa8312da759ab97f646a9fb6144462a115393b5f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2431666Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70150}