Revert of Concurrent sweeping of code space. (patchset #4 id:60001 of https://codereview.chromium.org/1222013002/)

Reason for revert:
[Sheriff] Increased flaky crashes. See:
https://code.google.com/p/v8/issues/detail?id=4275

Original issue's description:
> Concurrent sweeping of code space.
>
> BUG=
>
> Committed: https://crrev.com/3050b52f57d652dc45c8baf416e174f22dc2c159
> Cr-Commit-Position: refs/heads/master@{#29456}

TBR=jochen@chromium.org,hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1223763003

Cr-Commit-Position: refs/heads/master@{#29475}