This reverts commit 80f10346.

Reason for revert: Breaks build: https://logs.chromium.org/logs/v8/buildbucket/cr-buildbucket/8837831932745482705/+/u/build/compile/stdout?format=raw

Original change's description:
> Reland "heap: Use generic flags for main-thread only flags"
>
> This is a reland of 2a8e2a9b
>
> Original change's description:
> > heap: Use generic flags for main-thread only flags
> >
> > BasicMemoryChunk flags should only be mutated from the main thread
> > when no concurrent task can access them. For that purpose it is enough
> > to use regular non-atomic flags as they are immutable while the GC is
> > running.
> >
> > Change-Id: I0a9f8ecb2eb2aafaf17e77626ae27604abd1b618
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3107230
> > Reviewed-by: Hannes Payer <hpayer@chromium.org>
> > Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#76471}
>
> Change-Id: Iaf495546f82291ab674537f5d39e10d0495ac612
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3117486
> Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#76506}

Change-Id: I2a20c6f70f796e7f869bb2c9be0f8e80a89c98cf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3122586
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76510}