Revert of [heap] Switch to 500k pages (patchset #24 id:780001 of https://codereview.chromium.org/2013713003/ )

Reason for revert:
Failures on waterfall:

e.g. http://build.chromium.org/p/client.v8/builders/V8%20Linux64%20TSAN/builds/11134

Original issue's description:
> [heap] Switch to 500k pages
>
> - Decrease regular heap object size to 300k, keeping the same ration (60%)
>   between this limit and page size.
>
> In a follow up, we can now get rid of the new space border page while
> keeping the 1M minimum new space size.
>
> Some results (v8.infinite_scroll; 3 runs):
> - evacuate.avg: +15.3% (1.4->1.2)
> - evacuate.max: +24.4% (2.4->1.8)
>
> BUG=chromium:581412
> LOG=N
> R=hpayer@chromium.org, ulan@chromium.org, yangguo@chromium.org
>
> Committed: https://crrev.com/ffe5c670e1559d11e7b252e15fec38765e7dbe4f
> Cr-Commit-Position: refs/heads/master@{#38533}

TBR=hpayer@chromium.org,ulan@chromium.org,yangguo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:581412

Review-Url: https://codereview.chromium.org/2229403003
Cr-Commit-Position: refs/heads/master@{#38537}