Remove serialized_ flags where there's only one thing to be serialized
and its pointer can be used instead.

Bug: v8:7790
Change-Id: I489bb3085cef574f81f417f950898d4348f8b9ab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1886911Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Auto-Submit: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64608}