Drive-by: Avoid unnecessary memset and clean up Init().

Bug: v8:12559
Change-Id: I6a79f42dd62b47397d70f92efec3b569ca664c3e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3404097Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78722}