Revert of Ignore test failure for mjsunit/for-in-opt in gc stress. (patchset #1 id:1 of https://codereview.chromium.org/1295513004/ )

Reason for revert:
This test should work.

Original issue's description:
> Ignore test failure for mjsunit/for-in-opt in gc stress.
>
> TBR=hablich@chromium.org
> BUG=v8:4381
>
> Committed: https://crrev.com/22cf0b591968b7b305094d386d6b10e6c0e723cc
> Cr-Commit-Position: refs/heads/master@{#30245}

TBR=hablich@chromium.org,yangguo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4381
LOG=n

Review URL: https://codereview.chromium.org/1419823009

Cr-Commit-Position: refs/heads/master@{#31559}