chore(scripts): remove obsolete Slack OBO verifier

[kevkantes]

Warning

NEEDS DISCUSSION

@sriaradhyula, this removes the one-off live Slack OBO verifier you introduced in #1401. Please confirm there is no remaining operator workflow that depends on it.

Description

Removes only scripts/verify-slack-obo.sh. The script has no current caller in CI, Make, Compose, Helm, source, or supported documentation; its sole external reference is the historical Spec 102 task list being removed by #2454.

The live Slack OBO implementation remains supported and unit-tested in ai_platform_engineering/integrations/slack_bot/utils/obo_exchange.py. The deleted helper is not aligned with the current exchange contract because it omits the required audience parameter and does not validate the minted token audience.

Related: #2444 (reference only; this PR does not close it).

Type of Change

• Bugfix
• New Feature
• Breaking Change
• Refactor
• Documentation
• Other: remove an unreferenced historical operator helper

Checks

• git diff --check main...HEAD
• Reference audit across CI, Make, Compose, Helm, source, supported docs, and scripts: no live references remain
• Confirmed the only retained reference is docs/docs/specs/102-comprehensive-rbac-tests-and-completion/tasks.md, a historical file retired by draft chore(repo): retire Spec Kit workflow and historical specs #2454

Checklist

• I have read the contributing guidelines
• Existing issues have been referenced
• Relevant automated tests pass or are not applicable to this deletion-only change
• Draft PR against main
• Commit carries the explicitly provided DCO sign-off: kevkantes <kkantesa@cisco.com>

[github-actions]

✅ No proprietary content detected. This PR is clear for review!