Track retained layout validity explicitly

src/widget/position/pad.rs

@@ -21,12 +21,6 @@ impl Widget for Pad {
             },
         }
     }
-
-    /// The padding is an offset from each edge, so a longer box pads the same
-    /// amount and the child takes what is left over.
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }
 
 pub struct Padding {