monitor-manager: Don't introspect "monitor-privacy-screen-changed"
It passes a MetaLogicalMonitor, which isn't introspected right now, so skip it completely. The entry point to the UI is handled via MetaDisplay, so it isn't needed.
This fixes the following warning:
:: Warning: Meta: (Signal)monitor-privacy-screen-changed: argument object: Unresolved type: 'MetaLogicalMonitor'