ci: remove redundant town-crier announce-pr producer

Town-crier now announces PRs via its GitHub App (installed org-wide),
which covers announce/resolve/consensus for every repo. This per-repo
producer workflow is now redundant and fires a SECOND /announce to the
bus on every Agent Review Requested label and push/synchronize event,
double-posting on every PR/label event. Removing it stops the
duplication; the App is the single producer going forward.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rn34Ujm47YgQedoudDFiJW

Author: jasperboerhof