Revert of Merge cellspace into old pointer space (patchset #8 id:180001 of https://codereview.chromium.org/1010803012/)

Reason for revert:
Causes test failures on ARM bots related to cells and write barriers.

Original issue's description:
> Merge cellspace into old pointer space
>
> BUG=
>
> Committed: https://crrev.com/4e7163ce05f135918205c7855ae60a48e5d46cc5
> Cr-Commit-Position: refs/heads/master@{#27707}

TBR=hpayer@chromium.org,balazs.kilvady@imgtec.com,yangguo@chromium.org,verwaest@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1053243003

Cr-Commit-Position: refs/heads/master@{#27711}