Revert of Add d8 API for spawning function on a new thread (Second try) (patchset #3 id:60001 of https://codereview.chromium.org/1195613003/)

Reason for revert:
Fails on V8 Linux - isolates (http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20isolates/builds/4128)

Original issue's description:
> Add d8 API for spawning function on a new thread (Second try)
>
> This API closely matches the Worker API. The differences:
>
> 1) The argument to the Worker constructor is a function to run, not a script.
> 2) Receiving a message from a worker is a synchronous API (as there is no event
> loop).
>
> The serialization done here is not robust as the real DOM implementation. For
> example, recursive data structures or otherwise duplicated objects are not
> allowed.
>
> BUG=chromium:497295
> R=jochen@chromium.org
> LOG=n
>
> Review URL: https://codereview.chromium.org/1185643004
>
> Cr-Commit-Position: refs/heads/master@{#29126}
>
> Committed: https://crrev.com/ec2eaf712ecee6b4891c0458f2397e04a1f9b339
> Cr-Commit-Position: refs/heads/master@{#29158}

TBR=jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:497295

Review URL: https://codereview.chromium.org/1191373005

Cr-Commit-Position: refs/heads/master@{#29161}