Revert of [wasm] Enable WASM by default (--expose-wasm=true). (patchset #2 id:20001 of https://codereview.chromium.org/2623743003/ )

Reason for revert:
arm64 gc stress:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20gc%20stress/builds/4424

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-Commit-Position: refs/heads/master@{#42197}
> Committed: https://chromium.googlesource.com/v8/v8/+/34b63f050b1a247bb64ddc91c967501ce04e011f

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/2626763002
Cr-Commit-Position: refs/heads/master@{#42199}