This reverts part of crrev.com/c/2413252 since std::unique_ptr does
not satisfy is_standard_layout; and is_standard_layout is needed
to use offsetof:

 error: offset of on non-standard-layout type [-Werror,-Winvalid-offsetof]

Fixed: v8:12721
Change-Id: Ifbb1235fc3b8d1d855d41a226117fed88c506078
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3540141Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79597}