This reverts commit 24286b8e.

Reason for revert: Re-staging the experimental flag for fuzzing

Original change's description:
> Revert "[rab/gsab] Temporarily stage --harmony-rab-gsab to enable fuzzing"
>
> This reverts commit b8f88be0.
>
> Reason: disabling an experimental feature in release branch
>
> Bug: v8:11111,v8:12870
> Change-Id: I6fbd6bdb318c0d25e69c04db208a0d5f2b9ebbd7
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3647357
> Auto-Submit: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80520}

Bug: v8:11111,v8:12870
Change-Id: I0a45ed5ce53010196949dda23773d152aa605846
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3647836
Commit-Queue: Marja Hölttä <marja@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#80576}