effects/private: Simplify "active-hidden" state by inheriting from "initial-hidden"

This does not fix anything per se, just strips some unnecessary lines
and extra ensures zero opacity to other items.

src/effects/private/qml/WindowHeapDelegate.qml

@@ -263,11 +263,7 @@ Item {
         },
         State {
             name: "active-hidden"
-            extend: "initial"
-            PropertyChanges {
-                target: thumb
-                opacity: 0
-            }
+            extend: "initial-hidden"
         }
     ]