Reverts "Add code for updating `focusedChild` when removing grandchildren from scope" (#136862)

Reverts flutter/flutter#136771
Initiated by: gspencergoog
This change reverts the following previous change:
Original Description:
## Description

This adds code to make sure that grandchildren are removed from the `focusedChild` of a scope when the child is detached.

## Related Issues
 - Fixes https://github.com/flutter/flutter/issues/136758

## Tests
 - Added regression test.

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

@@ -964,13 +964,7 @@ class FocusNode with DiagnosticableTreeMixin, ChangeNotifier {
     assert(node._manager == _manager);
 
     if (removeScopeFocus) {
-      final FocusScopeNode? nodeScope = node.enclosingScope;
-      if (nodeScope != null) {
-        nodeScope._focusedChildren.remove(node);
-        node.descendants.where((FocusNode descendant) {
-          return descendant.enclosingScope == nodeScope;
-        }).forEach(nodeScope._focusedChildren.remove);
-      }
+      node.enclosingScope?._focusedChildren.remove(node);
     }
 
     node._parent = null;

packages/flutter/test/widgets/focus_manager_test.dart

@@ -459,46 +459,6 @@ void main() {
       expect(child2.hasPrimaryFocus, isTrue);
     });
 
-    // Regression test for https://github.com/flutter/flutter/issues/136758
-    testWidgetsWithLeakTracking('removing grandchildren from scope updates focusedChild', (WidgetTester tester) async {
-      final BuildContext context = await setupWidget(tester);
-
-      // Sets up this focus node tree:
-      //
-      //  root
-      //   |
-      // scope1
-      //   |
-      // child1
-      //   |
-      // child2
-      final FocusScopeNode scope1 = FocusScopeNode(debugLabel: 'scope2');
-      addTearDown(scope1.dispose);
-      final FocusAttachment scope2Attachment = scope1.attach(context);
-      scope2Attachment.reparent(parent: tester.binding.focusManager.rootScope);
-
-      final FocusNode child1 = FocusNode(debugLabel: 'child2');
-      addTearDown(child1.dispose);
-      final FocusAttachment child2Attachment = child1.attach(context);
-
-      final FocusNode child2 = FocusNode(debugLabel: 'child3');
-      addTearDown(child2.dispose);
-      final FocusAttachment child3Attachment = child2.attach(context);
-
-      child2Attachment.reparent(parent: scope1);
-      child3Attachment.reparent(parent: child1);
-      expect(child1.parent, equals(scope1));
-      expect(scope1.children.first, equals(child1));
-      child2.requestFocus();
-      await tester.pump();
-      expect(scope1.focusedChild, equals(child2));
-
-      // Detach the middle child and make sure that the scope is updated so that
-      // it no longer references child2 as the focused child.
-      child2Attachment.detach();
-      expect(scope1.focusedChild, isNull);
-    });
-
     testWidgetsWithLeakTracking('Requesting focus before adding to tree results in a request after adding', (WidgetTester tester) async {
       final BuildContext context = await setupWidget(tester);
       final FocusScopeNode scope = FocusScopeNode();