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/+/2432087Reviewed-by: Francis McCabe <fgm@chromium.org>
Commit-Queue: Francis McCabe <fgm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70142}