This reverts commit 61195eb6.

Reason for revert: breaks gc stress

Original change's description:
> [in-place weak refs] Replace the WeakCell potentially in Map::raw_transitions_.
> 
> BUG=v8:7308
> 
> Change-Id: I3021df5f6dfd02d85ed9fe1903f9c0850f92168d
> Reviewed-on: https://chromium-review.googlesource.com/972962
> Commit-Queue: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52272}

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

Change-Id: I218b4d767da5095e5c5fee650567eb41343b347e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7308
Reviewed-on: https://chromium-review.googlesource.com/983812Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52275}