This reverts commit 0cd7468b.

Reason for revert: Blocks v8 roll into chromium: https://crbug.com/828499

Original change's description:
> [wasm] Always enable guard regions on 64-bit platforms
> 
> This change makes full 8 GiB guard regions always enabled on 64-bit
> platforms.
> 
> Additionally, since all Wasm memory allocation paths have some form of
> guard regions, this removes and simplifies most of the logic around
> whether to enable guard regions.
> 
> R=​gdeepti@chromium.org
> 
> Change-Id: Idf3fbcc11ac70ea2ee7eb88c2173d6a1410395e1
> Reviewed-on: https://chromium-review.googlesource.com/985142
> Commit-Queue: Eric Holk <eholk@chromium.org>
> Reviewed-by: Brad Nelson <bradnelson@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52310}

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

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I126b5afe283a4fe08adfa301e637d2641c29cccd
Reviewed-on: https://chromium-review.googlesource.com/993160Reviewed-by: Eric Holk <eholk@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52334}