Since flags are statically stored, there's no difference between
the first runs and the second last run in stress-opt mode. This
simplifies the code to account for that.

Bug: v8:9940
Change-Id: Icc978f20476c0dffb084f7e9e6a200a5608e3515
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1898659Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64756}