Revert of Reland "[heap] Start sweeper tasks after evacuation. (patchset #2 id:20001 of https://chromiumcoder… (patchset #1 id:1 of https://chromiumcodereview.appspot.com/2437873004/ )

Reason for revert:
Canary crashes crbug.com/658718

Original issue's description:
> Reland "[heap] Start sweeper tasks after evacuation. (patchset #2 id:20001 of https://chromiumcodereview.appspot.com/2428043002/ )"
>
> The performance regression in crbug.com/657776 was not caused by this CL.
>
> This reverts commit 4490a760.
>
> BUG=

TBR=mlippautz@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=

Review-Url: https://codereview.chromium.org/2446583003
Cr-Commit-Position: refs/heads/master@{#40539}