Revert of Add the concept of a V8 extras exports object (patchset #5 id:80001 of https://codereview.chromium.org/1128113006/)

Reason for revert:
[Sheriff] Causes gc stress failures:
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20gc%20stress/builds/2167

Original issue's description:
> Add the concept of a V8 extras exports object
>
> Exposed to the extras as extrasExports (on the builtins object), on
> which they can put things that should be accessible from C++. Exposed
> to C++ through the V8 API as v8::Context::GetExtrasExportsObject().
>
> Adding a test (in test-api.cc) required adding a simple extra,
> test-extra.js, which we build into the standalone builds.
>
> R=yangguo@chromium.org, jochen@chromium.org
> BUG=
>
> Committed: https://crrev.com/ad547cea05f3e02c67243b682e933fc53ac763d9
> Cr-Commit-Position: refs/heads/master@{#28317}

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

Review URL: https://codereview.chromium.org/1127313005

Cr-Commit-Position: refs/heads/master@{#28332}