Remove new unused elements (#44551)

Author: srawlins

packages/flutter/lib/src/cupertino/context_menu.dart

@@ -868,8 +868,6 @@ class _ContextMenuRouteStaticState extends State<_ContextMenuRouteStatic> with T
   static const double _kDamping = 400.0;
   static const Duration _kMoveControllerDuration = Duration(milliseconds: 600);
 
-  final GlobalKey _childGlobalKey = GlobalKey();
-
   Offset _dragOffset;
   double _lastScale = 1.0;
   AnimationController _moveController;

packages/flutter/lib/src/gestures/multitap.dart

@@ -43,11 +43,10 @@ typedef GestureMultiTapCancelCallback = void Function(int pointer);
 class _CountdownZoned {
   _CountdownZoned({ @required Duration duration })
        : assert(duration != null) {
-    _timer = Timer(duration, _onTimeout);
+    Timer(duration, _onTimeout);
   }
 
   bool _timeout = false;
-  Timer _timer;
 
   bool get timeout => _timeout;
 

packages/flutter/lib/src/semantics/semantics.dart

@@ -2595,7 +2595,6 @@ class SemanticsOwner extends ChangeNotifier {
   final Set<SemanticsNode> _dirtyNodes = <SemanticsNode>{};
   final Map<int, SemanticsNode> _nodes = <int, SemanticsNode>{};
   final Set<SemanticsNode> _detachedNodes = <SemanticsNode>{};
-  final Map<int, CustomSemanticsAction> _actions = <int, CustomSemanticsAction>{};
 
   /// The root node of the semantics tree, if any.
   ///