Web platform tests that allocate 600 memories fail due to this. (This seems to also interfere with tests on the same shard).

This reverts commit b9abc7f0.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> [wasm] Enable guards on 64-bit systems.
> 
> R=​eholk@chromium.org
> 
> Bug: 
> Change-Id: Ia099cf085510da50a87b9f999020d6a66d6eab20
> Reviewed-on: https://chromium-review.googlesource.com/838250
> Commit-Queue: Brad Nelson <bradnelson@chromium.org>
> Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Eric Holk <eholk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50300}

TBR=bradnelson@chromium.org,eholk@chromium.org,clemensh@chromium.org

Change-Id: Ie7fc2a2142bddb03df41a5b705087a2e1f03e163
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/842925Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50304}