This reverts commit c823ca95.

Reason for revert: test failures

Original change's description:
> [csa] Add TNode<MaybeObject>.
> 
> LoadMaybeWeakField returns a TNode<MaybeObject>, and the only way to extract
> values from it is through explicit functions.
> 
> BUG=v8:7308
> 
> Change-Id: I98da6b715527bb9976b4c78ed9caaa39fbcb3ed5
> Reviewed-on: https://chromium-review.googlesource.com/1014106
> Commit-Queue: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52732}

TBR=marja@chromium.org,petermarshall@chromium.org,tebbi@chromium.org

Change-Id: Ie7ff36d39db1fedf668c21ed56532e364e93eca1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7308
Reviewed-on: https://chromium-review.googlesource.com/1024150Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52735}