ci(governance): delete retired scorecard-enforcer.yml (finishes refresh)

Final piece of the standards-pin refresh. #38/#39 squash-merged before this
deletion landed, so main still carries scorecard-enforcer.yml while both
reusable pins are already at @5a93d9d5. Removing the retired enforcer clears the
last `governance / Check Workflow Staleness` errors (retired enforcer + its
SARIF-to-Code-Scanning upload) and the matching Hypatia scorecard_publish_with_run_step finding.

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

Author: claude