This reverts commit de964dbe.

Reason for revert:
https://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/17958

Original change's description:
> Introducing an event loop mechanism for d8.
> 
> This mechanism ensures APIs like wasm async complete their work, 
> without requiring use of natives (%APIs).
> 
> The mechanism is similar to the one used in content_shell,
> which should allow us to easily port tests in that environment.
> 
> Review-Url: https://codereview.chromium.org/2842843005
> Cr-Original-Commit-Position: refs/heads/master@{#44908}
> Bug: 
> Change-Id: I9deee0d256a600c60b42902fc8ef8478e5546344
> Reviewed-on: https://chromium-review.googlesource.com/494968
> Commit-Queue: Mircea Trofin <mtrofin@google.com>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45165}

TBR=bradnelson@chromium.org,mtrofin@chromium.org,mtrofin@google.com,jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: Iafec2615d705d1990c57229cab3a988c00b5e12f
Reviewed-on: https://chromium-review.googlesource.com/498630Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45166}