This reverts commit 86038ecf.

Reason for revert: Caused TSAN failures

Original change's description:
> [heap] Optimize time to reach global safepoint
>
> Initial support for global safepoints kept it simple by entering a
> safepoint for each of them one after another. This means
> time-to-global-safepoint is the sum of all time-to-safepoint operations.
> We can improve this slightly by splitting up the safepoint iteration
> into two operations:
>
> 1) Initiate safepoint lock (locks local_heaps_mutex_, arms the barrier
>    and sets SafepointRequested flag for all client threads)
> 2) Block until all runnning client threads reach a safepoint
>
> We now perform operation 1) for all clients first and only then start
> with operation 2).
>
> Bug: v8:11708
> Change-Id: Iaafd3c6d70bcf7026f722633e9250b04148b3da6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3310910
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78308}

Bug: v8:11708, v8:12492
Change-Id: I32ef7139d4392adfadeffeb70c06f3ed18109ca8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3328782
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78328}