This reverts commit a1838956.

Reason for revert: https://bugs.chromium.org/p/v8/issues/detail?id=12642

Original change's description:
> [heap] Allow shared references in WeakMap
>
> Shared references can also be stored in WeakMaps and during marking we
> need to be able to deal with such references. In a client GC shared
> objects are treated as live, so we don't need to update or check mark
> bits for such objects.
>
> Bug: v8:11708
> Change-Id: I0dbf797472c4779f462750dab63cc9b012aad091
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3447365
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#79153}

Bug: v8:11708
Change-Id: I113672aceba0ef5aa71f6fbedda7e0df854a437d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3474673
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Owners-Override: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79168}