basic_subclass: remove useless code

We already have access to the private part of the object.

src/bin/basic_subclass.rs

@@ -165,10 +165,8 @@ impl ApplicationImpl for SimpleApplicationPrivate {
     // `gio::Application::activate` is what gets called when the
     // application is launched by the desktop environment and
     // aksed to present itself.
-    fn activate(&self, app: &gio::Application) {
-        let app = app.downcast_ref::<gtk::Application>().unwrap();
-        let priv_ = SimpleApplicationPrivate::from_instance(app);
-        let window = priv_
+    fn activate(&self, _app: &gio::Application) {
+        let window = self
             .window
             .get()
             .expect("Should always be initiliazed in gio_application_startup");
@@ -187,10 +185,8 @@ impl ApplicationImpl for SimpleApplicationPrivate {
         self.parent_startup(app);
 
         let app = app.downcast_ref::<gtk::Application>().unwrap();
-        let priv_ = SimpleApplicationPrivate::from_instance(app);
         let window = SimpleWindow::new(&app);
-        priv_
-            .window
+        self.window
             .set(window)
             .expect("Failed to initialize application window");
     }