Remove overheard.ron (1629 lines) and overheard.yaml.deprecated. D-078 overheard system is retired — the content and production pipeline for ambient NPC dialogue is deferred until the world is walkable (Phase 6). Deep module interdependencies (perception, simulation, bridge) mean the server-side plumbing stays in place; only the content files with no live consumers are removed. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>