Revert of Enable per thread heap for database thread (patchset #12 id:220001 of https://codereview.chromium.org/1909813002/ )

Reason for revert:
This CL is causing a top #1 crasher.

https://bugs.chromium.org/p/chromium/issues/detail?id=617141

Original issue's description:
> Enable per thread heap for database thread
>
> BUG=591606
>
> Committed: https://crrev.com/993e3a74102e0843bebb2f52de1a904f151843d4
> Cr-Commit-Position: refs/heads/master@{#397383}

TBR=oilpan-reviews@chromium.org,keishi@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=591606

Review-Url: https://codereview.chromium.org/2037233002
Cr-Commit-Position: refs/heads/master@{#397884}
14 files changed