Revert of Replace ad-hoc weakness in prototype transitions with WeakCell. (patchset #2 id:20001 of https://codereview.chromium.org/1163073002/)

Reason for revert:
GC stress failures.

Original issue's description:
> Replace ad-hoc weakness in prototype transitions with WeakCell.
>
> BUG=
>
> Committed: https://crrev.com/bfb81fbe0d38c88cc1b6ed6eb1a4b8cbe2c469c3
> Cr-Commit-Position: refs/heads/master@{#28830}

TBR=jkummerow@chromium.org,hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1169733002

Cr-Commit-Position: refs/heads/master@{#28832}