This reverts commit e9750cb8.

Reason for revert: Several GC failures, e.g. https://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/23236, https://build.chromium.org/p/client.v8/builders/V8%20Mac/builds/18390 

Original change's description:
> Preempt ConcurrentMarking tasks instead of merely pausing in PauseScope.
> 
> Follow-up to https://chromium-review.googlesource.com/c/v8/v8/+/924867
> 
> This is the core goal of the initial CL @
> https://chromium-review.googlesource.com/c/v8/v8/+/922103
> which was since split into multiple to diagnose a bots-only failure.
> 
> Bug: chromium:812178
> Change-Id: I4c4e0b517737e020862917bd89fa6ce38244e597
> Reviewed-on: https://chromium-review.googlesource.com/924031
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51356}

TBR=gab@chromium.org,ulan@chromium.org,mlippautz@chromium.org

Change-Id: Ic095e32708e58acbe5955bf29e65af34c59d321e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:812178
Reviewed-on: https://chromium-review.googlesource.com/925301Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51363}