#951 Drop local tool rate-limit counters (tool_rate_limit_usage + consume/check/cleanup SQL functions) after TokenGate path verified in production

EARS: When the TokenGate tool-limit path (#928) has run in production with no fail-closed incidents for 7 days, the system shall drop highway.tool_rate_limit_usage, highway.consume_tool_rate_token, highway.check_tool_rate_quota and highway.cleanup_tool_rate_limit_usage via a migretti migration in highway-core, and remove tests/unit/db/test_tool_rate_limit_integration.py TestDatabaseSchema/TestTokenConsumption. Deferred from #928 so an image rollback keeps a working (old) code path.