test: remove test/v8-updates/test-postmortem-metadata.js

The postmortem metadata test is no longer used to maintain
postmortem debugging tools. Since it frequently breaks on
V8 updates, it makes more sense to just remove it.

Backport-PR-URL: #34356
PR-URL: #33579
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>

Author: cjihrig