This reverts commit 6af43874.

Reason for revert: Linux TSAN failures:

https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20TSAN/builds/19028

Original change's description:
> [heap] Remove page header tag from owner field.
> 
> Bug: chromium:800251
> Change-Id: I101131b4651b0bb27a79e5107ee43caf1229ffc7
> Reviewed-on: https://chromium-review.googlesource.com/860010
> Commit-Queue: Hannes Payer <hpayer@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50507}

TBR=ulan@chromium.org,hpayer@chromium.org

Change-Id: I29001423959f6d9faadbdba5228b28cfb1f5b341
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:800251
Reviewed-on: https://chromium-review.googlesource.com/861923Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50512}