Some post-compile flag setting was unnecessary, since those flags
originally came from the SFI they were being set on.

Also, DontOptimizeReason was never actually set, so we can remove it
entirely.

Change-Id: Ic07821fc20ba4e16a2bd8b9e8ac8c1b266aa4067
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3260510
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77702}