Revert of Enable parallel pointer updates after evacuation. (patchset #1 id:1 of https://codereview.chromium.org/1784643010/ )

Reason for revert:
Speculative revert to check if this CL is causing GC stress failures.

Original issue's description:
> Enable parallel pointer updates after evacuation.
>
> BUG=chromium:578883
> LOG=NO
>
> Committed: https://crrev.com/7217fcc0bf5b0f62947f92128ec76855d50e91da
> Cr-Commit-Position: refs/heads/master@{#34712}

TBR=mlippautz@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:578883
LOG=NO

Review URL: https://codereview.chromium.org/1803573002

Cr-Commit-Position: refs/heads/master@{#34741}