Do not send notification about device suspending

Mobian on the PinePhone uses the device LED to indicate new notifications. Since a notification is sent about the device going to sleep soon, the LED starts flashing, making the user think they've gotten a legitimate notification.

This behaviour is understandable on a desktop or a laptop, but a phone's suspend is expected to be seamless and a user typically doesn't think of their phone "going to sleep" when not using it: it implies inactivity which can fool the user into thinking they won't be receiving calls or texts when their phone is asleep. This notification just leads to confusion and should, if possible, be removed.