allowed-apns plugin will try to uregister the AllowedAccessPoints
interface whenever the sim state changes, even when not registered.
This results in the (benign) error being printed inside
ofono_modem_remove_interface:
Interface org.ofono.AllowedAccessPoints not found on the interface_list
When a modem is being removed, all of the modem's atom watches have
already been cleaned up. Trying to remove it again results in a crash.
Fix by registering a destroy callback which will be notified when the
atomwatch has been removed.
Denis Kenzior
Alexander Couzens
Nishanth V