network: Ensure devices are removed from UI when disappearing

The "removed" callback from NMObject is never called when the object is
simply finalised because the UI drops the reference. Explicitly call the
handler so that UI elements are removed.

panels/network/cc-network-panel.c

@@ -556,6 +556,8 @@ panel_remove_device (CcNetworkPanel *panel, NMDevice *device)
         if (object == NULL)
                 return;
 
+        /* NMObject will not fire the "removed" signal, so handle the UI removal explicitly */
+        object_removed_cb (object, panel);
         g_ptr_array_remove (panel->devices, object);
 
         /* update vpn widgets */