This reverts commit 20f33823.

Reason for revert: Fails on win32: https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Win32/14437

Original change's description:
> [wasm] Enable Liftoff by default on ia32 and x64
> 
> R=​titzer@chromium.org, hablich@chromium.org
> 
> Bug: v8:6600, chromium:787421
> Change-Id: Ia8ae56ddef3b27b0721d5a66ff19abe098a2c6ca
> Reviewed-on: https://chromium-review.googlesource.com/1109899
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Reviewed-by: Michael Hablich <hablich@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#53965}

TBR=titzer@chromium.org,hablich@chromium.org,clemensh@chromium.org

Change-Id: I0edc228a88bc74624338852826a90f1f9b6eda0b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6600, chromium:787421
Reviewed-on: https://chromium-review.googlesource.com/1112017Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53967}