This reverts commit 3cb4039c.

Reason for revert: TSAN failure in newly added test: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20isolates/18086/overview

Original change's description:
> [string] Support shared strings in Value{Serializer,Deserializer}
>
> When FLAG_shared_string_table is true, postMessaging strings will share
> instead of copy.
>
> Note that not all operations on shared strings are supported, and shared
> strings may be slower than non-shared strings for some operations.
>
> Bug: v8:12007
> Change-Id: I3462128e15410d2568868143571571b3025722c1
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3277250
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Shu-yu Guo <syg@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78614}

Bug: v8:12007
Change-Id: I5bb8f9b4e9b641c6d5cb16f963e9dbc1b13ac56a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3386799
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78615}