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/+/3599481Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Benoit Lize <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80106}