hwmontempsensor doesn't notice card removals

[spinler]

It isn't watching for an InterfacesRemoved signal from entity-manager, so it doesn't realize the device went away and still tries to read it anyway, so it treats it like an error.

Ideally, it should remove the sensor from D-Bus in that case as discussed on discord.

This actually goes for every application in the same repo, since I don't see any InterfacesRemoved watches at all, but as my company only uses hwmontempsensor at the moment it's the only one I can fix, and the code between them isn't common enough to fix it all in one place.

I plan on making this change. Just opening an issue for general awareness.