ci(governance): drop retired scorecard-enforcer.yml (completes 3-edit refresh)

#38 squash-merged at f853278, before the governance changes, so main still
carries scorecard-enforcer.yml and the stale pins. This branch already bumped
the two reusable pins; delete the retired enforcer here too so #39 lands the
complete refresh and the staleness check goes green (also clears the Hypatia
scorecard_publish_with_run_step + SARIF-to-Code-Scanning findings that live in
that file).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LvsZgNxFbeqfRmrVFNhJ8G

Author: claude