This reverts commit 61d42c94.

Reason for revert: TSan failures: https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux64%20TSAN/23459

Original change's description:
> Use std::atomic in Cancelable
> 
> Avoid deprecated base::AtomicValue, use std::atomic instead.
> Plus minor drive-by cleanups.
> 
> R=​mstarzinger@chromium.org
> 
> Bug: v8:8238
> Change-Id: I47a1f00e26a843b60380c50399eedc49d859830a
> Reviewed-on: https://chromium-review.googlesource.com/c/1326463
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#57386}

TBR=ulan@chromium.org,mstarzinger@chromium.org,clemensh@chromium.org

Change-Id: I96f269800eb9c26812050629f7f2c75096f3c858
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8238
Reviewed-on: https://chromium-review.googlesource.com/c/1329201Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57387}