This reverts commit 6af09b1b.

Reason for revert: Breaks Win debug builder - https://ci.chromium.org/p/v8/builders/ci/V8%20Win32%20-%20debug/26384?

Original change's description:
> [offthread] Add a write lock to the string table
> 
> Adds an initial implementation of a concurrency support for the string
> table, allowing it to be read without holding a lock, and written to
> while holding a lock.
> 
> This is an initial prototype of _roughly_ how the concurrency would
> work; there are still a few holes (e.g. around deserialization). This
> is predominantly to assess the main-thread runtime impact of the more
> complex string table access.
> 
> Bug: v8:10729
> Change-Id: I5c6c35e6fca309efd6ee79804c16972aae1ab3ab
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2306804
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#68985}

TBR=ulan@chromium.org,leszeks@chromium.org,ishell@chromium.org,verwaest@chromium.org

Change-Id: I001dc81f1d4031bf0451766452a43176df997354
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10729
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2312776Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68988}