Revert of [heap] Turn on parallel compaction

Revert of [heap] Turn on parallel compaction (patchset #1 id:1 of https://codereview.chromium.org/1364693002/ )

Reason for revert:
Fails on gc stress
  https://chromegw.corp.google.com/i/client.v8/builders/V8%20Linux%20-%20gc%20stress/builds/157/

Original issue's description:
> [heap] Turn on parallel compaction
>
> R=hpayer@chromium.org
> BUG=chromium:524425
> LOG=N
>
> Committed: https://crrev.com/04db5bfa915766b228218ddc748af308b57ae8ea
> Cr-Commit-Position: refs/heads/master@{#31763}

TBR=hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:524425
Committed: https://crrev.com/e682048027b51dea5b1c9a970e09b8b2a99fcae6
Cr-Commit-Position: refs/heads/master@{#31765}

[Michael Lippautz, 2015-11-03 23:24:04]

Created Revert of [heap] Turn on parallel compaction

[commit-bot: I haz the power, 2015-11-03 23:24:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1424313008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1424313008/1

[commit-bot: I haz the power, 2015-11-03 23:24:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-03 23:24:39]

Patchset 1 (id:??) landed as
https://crrev.com/e682048027b51dea5b1c9a970e09b8b2a99fcae6
Cr-Commit-Position: refs/heads/master@{#31765}