This reverts commit ad221d14.

Reason for revert: Layout test failures:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/22780

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.
> 
> This is a reland of https://crrev.com/c/985142.
> 
> Bug: v8:7619
> Change-Id: I8bf1f86d6f89fd0bb2144431c7628f15a6b00ba0
> Reviewed-on: https://chromium-review.googlesource.com/996466
> Reviewed-by: Brad Nelson <bradnelson@chromium.org>
> Commit-Queue: Eric Holk <eholk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52412}

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

Change-Id: Ic15d14c6fa69300bc0fdc036b9fee8ecf65fd397
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7619
Reviewed-on: https://chromium-review.googlesource.com/999412Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52418}