cleanup

packages/stream_chat_flutter_core/test/stream_channel_test.dart

@@ -284,10 +284,3 @@ void main() {
     },
   );
 }
-
-class MockStreamChannelState extends Mock implements StreamChannelState {
-  @override
-  String toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) {
-    return super.toString();
-  }
-}