Revert "Assert when duplicated keys are introduced in subsequent build (#81850)" (#82039)

This reverts commit 3ab799bb.

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

@@ -6304,7 +6304,6 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
   void update(MultiChildRenderObjectWidget newWidget) {
     super.update(newWidget);
     assert(widget == newWidget);
-    assert(!debugChildrenHaveDuplicateKeys(widget, widget.children));
     _children = updateChildren(_children, widget.children, forgottenChildren: _forgottenChildren);
     _forgottenChildren.clear();
   }

packages/flutter/test/widgets/framework_test.dart

@@ -512,9 +512,11 @@ void main() {
     expect(
       exception.toString(),
       equalsIgnoringHashCodes(
-        'Duplicate keys found.\n'
-        'If multiple keyed nodes exist as children of another node, they must have unique keys.\n'
-        'Stack(alignment: AlignmentDirectional.topStart, textDirection: ltr, fit: loose) has multiple children with key [GlobalKey#00000 problematic].'
+        'Multiple widgets used the same GlobalKey.\n'
+        'The key [GlobalKey#00000 problematic] was used by 2 widgets:\n'
+        '  SizedBox-[GlobalKey#00000 problematic]\n'
+        '  Placeholder-[GlobalKey#00000 problematic]\n'
+        'A GlobalKey can only be specified on one widget at a time in the widget tree.',
       ),
     );
   });
@@ -539,9 +541,11 @@ void main() {
     expect(
       exception.toString(),
       equalsIgnoringHashCodes(
-        'Duplicate keys found.\n'
-        'If multiple keyed nodes exist as children of another node, they must have unique keys.\n'
-        'Stack(alignment: AlignmentDirectional.topStart, textDirection: ltr, fit: loose) has multiple children with key [GlobalKey#00000 problematic].'
+        'Multiple widgets used the same GlobalKey.\n'
+        'The key [GlobalKey#00000 problematic] was used by 2 widgets:\n'
+        '  Container-[GlobalKey#00000 problematic]\n'
+        '  Placeholder-[GlobalKey#00000 problematic]\n'
+        'A GlobalKey can only be specified on one widget at a time in the widget tree.',
       ),
     );
   });

packages/flutter/test/widgets/multichildobject_with_keys_test.dart

@@ -58,57 +58,6 @@ void main() {
       <String>['0', '6', '7', '8', '1', '2', '3', '4', '5'],
     );
   });
-
-  testWidgets('Building a new MultiChildRenderObjectElement with children having duplicated keys throws', (WidgetTester tester) async {
-    const ValueKey<int> duplicatedKey = ValueKey<int>(1);
-
-    await tester.pumpWidget(Column(
-      children: const <Widget>[
-        Text('Text 1', textDirection: TextDirection.ltr, key: duplicatedKey),
-        Text('Text 2', textDirection: TextDirection.ltr, key: duplicatedKey),
-      ],
-    ));
-
-    expect(
-      tester.takeException(),
-      isA<FlutterError>().having(
-        (FlutterError error) => error.message,
-        'error.message',
-        startsWith('Duplicate keys found.'),
-      ),
-    );
-  });
-
-  testWidgets('Updating a MultiChildRenderObjectElement to have children with duplicated keys throws', (WidgetTester tester) async {
-    // Regression test for https://github.com/flutter/flutter/issues/81541
-
-    const ValueKey<int> key1 = ValueKey<int>(1);
-    const ValueKey<int> key2 = ValueKey<int>(2);
-
-    Future<void> _buildWithKey(Key key) {
-      return tester.pumpWidget(Column(
-        children: <Widget>[
-          const Text('Text 1', textDirection: TextDirection.ltr, key: key1),
-          Text('Text 2', textDirection: TextDirection.ltr, key: key),
-        ],
-      ));
-    }
-
-    // Initial build with two different keys.
-    await _buildWithKey(key2);
-    expect(tester.takeException(), isNull);
-
-    // Subsequent build with duplicated keys.
-    await _buildWithKey(key1);
-    expect(
-      tester.takeException(),
-      isA<FlutterError>().having(
-        (FlutterError error) => error.message,
-        'error.message',
-        startsWith('Duplicate keys found.'),
-      ),
-    );
-  });
 }
 
 // Do not use tester.renderObjectList(find.byType(RenderParagraph). That returns