This reverts commit 4b49f844.

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:
> Add a trace event when pausing/preempting concurrent marking.
> 
> This will let us identify in traces whether unwinding after receiving
> the preemption event is slower than desired and should be optimized.
> 
> Adding it to pausing while working on removing it in
> https://chromium-review.googlesource.com/c/v8/v8/+/922103
> will allow gathering traces that highlight the issue.
> 
> R=​mlippautz@chromium.org
> 
> Bug: chromium:812178
> Change-Id: I0555c6825e0792769c9ae2d748d7cc35df4f6fed
> Reviewed-on: https://chromium-review.googlesource.com/924122
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51354}

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

Change-Id: I37a82e488de51d5ae4d7ed795b82ea9649c4a5f9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:812178
Reviewed-on: https://chromium-review.googlesource.com/924426Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51364}