Revert of [heap] Switch to 500k pages (patchset #5 id:80001 of https://codereview.chromium.org/2314803002/ )

Reason for revert:
Breaks arm64 nosnap debug:
https://build.chromium.org/p/client.v8.ports/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20nosnap%20-%20debug/builds/2178

Original issue's description:
> [heap] Switch to 500k pages
>
> BUG=chromium:636331
> R=ulan@chromium.org
>
> Committed: https://crrev.com/4b618dbf8ec7f0edf377b54b48bf3c852d5e235a
> Cr-Commit-Position: refs/heads/master@{#39220}

TBR=ulan@chromium.org,mlippautz@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:636331

Review-Url: https://codereview.chromium.org/2312853005
Cr-Commit-Position: refs/heads/master@{#39229}