This reverts commit 3ee4804f.

Reason for revert: breaks blink_unit_tests:
https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Blink%20Linux/15074/overview

Original change's description:
> [top-level-await] Remove --harmony-top-level-await
>
> TLA has been shipped since v8.9.
>
> Bug: v8:9344, chromium:1271114
> Change-Id: Ibebf21da8bacb1f0d212390133847495ad8553e5
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3307103
> Commit-Queue: Shu-yu Guo <syg@chromium.org>
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78169}

Bug: v8:9344, chromium:1271114
Change-Id: I0874bcaba18fde3b48f5ef7eeae89f2fa4978d51
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3308422
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78170}