session: remove nm-applet from required components (it's not)

nm-applet is not used by Cinnamon since it has it's own network applet on this path:
/usr/share/cinnamon/applets/network@cinnamon.org

The nm-applet systray icon is hidden anyway by the systray applet. It's D-Bus API is not used either. There is no reason to have it in required components.