This commit updates the gen-postmortem-metadaa.py script to
incorporate changes in V8 8.5. This removes the need to float a
patch to the script in Node.js.

Change-Id: I6532495bee906f51eb2b773ec38ff0a6e404dafe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2582705Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/master@{#71699}