bluetooth: Deregister battery provider when profile disconnects

Whenever a device disconnects the device is not removed from BlueZ, only
the profiles that had an active connection are disconnected. Since we
were providing this battery level based on AT commands received through
HSP/HFP these services should be responsible for deregistering it again.

Deregister the interface to signal BlueZ (And UPower in return) that the
battery level won't be accurate/updated anymore.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/482>

src/modules/bluetooth/backend-native.c

@@ -686,6 +686,11 @@ static void rfcomm_io_callback(pa_mainloop_api *io, pa_io_event *e, int fd, pa_i
 
     if (events & (PA_IO_EVENT_HANGUP|PA_IO_EVENT_ERROR)) {
         pa_log_info("Lost RFCOMM connection.");
+        // TODO: Keep track of which profile is the current battery provider,
+        // only deregister if it is us currently providing these levels.
+        // (Also helpful to fill the 'Source' property)
+        // We might also move this to Profile1::RequestDisconnection
+        pa_bluetooth_device_deregister_battery(t->device);
         goto fail;
     }