Revert of [heap] Add more tasks for parallel compaction (patchset #11 id:200001 of https://codereview.chromium.org/1354383002/ )

Reason for revert:
[Sheriff] May have caused this new flake:
http://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/5412

Original issue's description:
> [heap] Add more tasks for parallel compaction
>
> - We now compute the number of parallel compaction tasks, depending on the
>   evacuation candidate list, the number of cores, and some hard limit.
> - Free memory is moved over to compaction tasks (up to some limit)
> - Moving over memory is done by dividing the free list of a given space up among
>   other free lists. Since this is potentially slow we limit the maximum amount
>   of moved memory.
>
> BUG=chromium:524425
> LOG=N
>
> Committed: https://crrev.com/0e842418835eea85886a06cf37052895bc8a17db
> Cr-Commit-Position: refs/heads/master@{#30886}

TBR=hpayer@chromium.org,mlippautz@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:524425

Review URL: https://codereview.chromium.org/1356363005

Cr-Commit-Position: refs/heads/master@{#30888}