This reverts commit abcb6bb8.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20isolates/20029/overview

Original change's description:
> [heap] Avoid dynamic updates of FLAG_gc_interval
>
> Flags will be protected from updates after V8 initialization (in the
> future). This CL avoids any updates of the --gc-interval flag during
> runtime, and instead updates a static field on the HeapAllocator
> directly.
>
> R=​mlippautz@chromium.org
>
> Bug: v8:12887
> Change-Id: I17a495cae50a46d59a8159c6ece1558d4d61b949
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3687691
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80998}

Bug: v8:12887
Change-Id: I18310a3f515506d617f42be7a208013957625eaf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695559Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Owners-Override: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81002}