Revert of [wasm] Enable WASM by default (--expose-wasm=true). (patchset #3 id:40001 of https://codereview.chromium.org/2623743003/ )

Reason for revert:
layout test breakages:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/12574

revert first to unblock rolling. otherwise please rebaseline.

Original issue's description:
> [wasm] Enable WASM by default (--expose-wasm=true).
>
> BUG=chromium:575167
> R=rossberg@chromium.org,ahaas@chromium.org,clemensh@chromium.org,bradnelson@chromium.org
>
> Review-Url: https://codereview.chromium.org/2623743003
> Cr-Original-Commit-Position: refs/heads/master@{#42197}
> Committed: https://chromium.googlesource.com/v8/v8/+/34b63f050b1a247bb64ddc91c967501ce04e011f
> Review-Url: https://codereview.chromium.org/2623743003
> Cr-Commit-Position: refs/heads/master@{#42214}
> Committed: https://chromium.googlesource.com/v8/v8/+/71f5650828ffd0162fcd67d9c6ef570a346a8a84

TBR=clemensh@chromium.org,ahaas@chromium.org,bradnelson@chromium.org,rossberg@chromium.org,bradnelson@google.com,titzer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:575167

Review-Url: https://codereview.chromium.org/2621323002
Cr-Commit-Position: refs/heads/master@{#42222}