Track retained layout validity explicitly

src/widget/image.rs

@@ -14,10 +14,6 @@ impl Widget for Image {
     fn size_hint(&self, axis: Axis) -> Option<Len> {
         Some(Len::px(self.handle.size().axis(axis)))
     }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }
 
 pub fn image<State: UiRsc>(image: impl LoadableImage) -> impl WidgetFn<State, Image> {