This reverts commit 9fe53c4f.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20isolates/17044/overview

Original change's description:
> [flags] Skip --random-seed in FlagList::Hash
>
> Node and friends use --random-seed to temporary reset the seed for
> predictable code-cache creation. To allow custom random seeds at runtime
> the flag is reset for encoding the FlagList::Hash in the snapshots.
>
> We will soon disallow changing flags via the API after V8 has been
> initialized. In order to make node work we will exclude --random-seed
> from the FlagList::Hash calculation.
>
> Drive-by-fix:
> * Lazily initialize flag_hash instead of calculating it after every call
>   to SetFlagsFromString / EnforceFlagImplications.
> * Simplify hash string source creation since out << flag now includes
>   the full flag information
>
> Bug: v8:12309
> Change-Id: I1a168f4702d8c4d160ff12fdbea881731e4ea8b6
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3218159
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#77345}

Bug: v8:12309
Change-Id: I5e431c3e3ccccaab2ef7aa025b51d42f837f08b9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3218979Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#77347}