This reverts commit 9cdee4f4.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Mac64%20-%20debug/38658/overview

Original change's description:
> [base/platform] Simplify fast TLS on macOS
>
> Since the TLS offset is constant across all supported OS releases, we
> no longer need to adjust it, nor to read it at runtime. This also aligns
> the code in V8 with what is done in Chromium.
>
> Change-Id: I0f3c54da39a776406083c897de888f06c61852b8
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3599481
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Benoit Lize <lizeb@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80106}

Change-Id: Ie6371c2ad12ed6f63be51b819083a7c0c4e22751
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3602502
Auto-Submit: Tobias Tebbi <tebbi@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Owners-Override: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80108}