Remove deprecated DefaultFocusTraversal widget (#51240)

Remove deprecated DefaultFocusTraversal widget

packages/flutter/lib/src/widgets/focus_traversal.dart

@@ -1713,87 +1713,6 @@ class _FocusTraversalGroupMarker extends InheritedWidget {
   bool updateShouldNotify(InheritedWidget oldWidget) => false;
 }
 
-/// A deprecated widget that describes the inherited focus policy for focus
-/// traversal for its descendants.
-///
-/// _This widget has been deprecated: use [FocusTraversalGroup] instead._
-@Deprecated(
-  'Use FocusTraversalGroup as a replacement for DefaultFocusTraversal. Be aware that FocusTraversalGroup does add an (unfocusable) Focus widget to the hierarchy that DefaultFocusTraversal does not. Use FocusTraversalGroup.of(context) as a replacement for DefaultFocusTraversal.of(context). '
-  'This feature was deprecated after v1.14.3.'
-)
-class DefaultFocusTraversal extends InheritedWidget {
-  /// Creates a [DefaultFocusTraversal] object.
-  ///
-  /// The [child] argument must not be null.
-  const DefaultFocusTraversal({
-    Key key,
-    this.policy,
-    @required Widget child,
-  }) : super(key: key, child: child);
-
-  /// The policy used to move the focus from one focus node to another when
-  /// traversing them using a keyboard.
-  ///
-  /// _This widget has been deprecated: use [FocusTraversalGroup] instead._
-  ///
-  /// If not specified, traverses in reading order using
-  /// [ReadingOrderTraversalPolicy].
-  ///
-  /// See also:
-  ///
-  ///  * [FocusTraversalPolicy] for the API used to impose traversal order
-  ///    policy.
-  ///  * [WidgetOrderTraversalPolicy] for a traversal policy that traverses
-  ///    nodes in the order they are added to the widget tree.
-  ///  * [ReadingOrderTraversalPolicy] for a traversal policy that traverses
-  ///    nodes in the reading order defined in the widget tree, and then top to
-  ///    bottom.
-  final FocusTraversalPolicy policy;
-
-  /// Returns the [FocusTraversalPolicy] that most tightly encloses the given
-  /// [BuildContext].
-  ///
-  /// _This method has been deprecated: use `FocusTraversalGroup.of(context)` instead._
-  ///
-  /// It does not create a rebuild dependency because changing the traversal
-  /// order doesn't change the widget tree, so nothing needs to be rebuilt as a
-  /// result of an order change.
-  ///
-  /// The [context] argument must not be null.
-  static FocusTraversalPolicy of(BuildContext context, {bool nullOk = false}) {
-    final DefaultFocusTraversal inherited = context.getElementForInheritedWidgetOfExactType<DefaultFocusTraversal>()?.widget as DefaultFocusTraversal;
-    assert(() {
-      if (nullOk) {
-        return true;
-      }
-      if (context == null) {
-        throw FlutterError(
-          'The context given to DefaultFocusTraversal.of was null, so '
-          'consequently no FocusTraversalGroup ancestor can be found.',
-        );
-      }
-      if (inherited == null) {
-        throw FlutterError(
-          'Unable to find a DefaultFocusTraversal widget in the context.\n'
-          'DefaultFocusTraversal.of() was called with a context that does not contain a '
-          'DefaultFocusTraversal.\n'
-          'No DefaultFocusTraversal ancestor could be found starting from the context that was '
-          'passed to DefaultFocusTraversal.of(). This can happen because there is not a '
-          'WidgetsApp or MaterialApp widget (those widgets introduce a DefaultFocusTraversal), '
-          'or it can happen if the context comes from a widget above those widgets.\n'
-          'The context used was:\n'
-          '  $context',
-        );
-      }
-      return true;
-    }());
-    return inherited?.policy ?? ReadingOrderTraversalPolicy();
-  }
-
-  @override
-  bool updateShouldNotify(DefaultFocusTraversal oldWidget) => false;
-}
-
 // A base class for all of the default actions that request focus for a node.
 class _RequestFocusActionBase extends Action {
   _RequestFocusActionBase(LocalKey name) : super(name);