Remove duplicate code comment in flutter_gallery (#23422)

examples/flutter_gallery/lib/demo/animation/home.dart

@@ -289,9 +289,6 @@ class _AllSectionsView extends AnimatedWidget {
   Widget _build(BuildContext context, BoxConstraints constraints) {
     final Size size = constraints.biggest;
 
-    // The layout's progress from from a column to a row. Its value is
-    // 0.0 when size.height equals the maxHeight, 1.0 when the size.height
-    // equals the midHeight.
     // The layout's progress from from a column to a row. Its value is
     // 0.0 when size.height equals the maxHeight, 1.0 when the size.height
     // equals the midHeight.