fix: import/export

packages/flutter_widgets/lib/stream_chat_flutter.dart

@@ -1,5 +1,3 @@
-export 'package:stream_chat/stream_chat.dart';
-
 export 'src/back_button.dart';
 export 'src/channel_header.dart';
 export 'src/channel_image.dart';

packages/flutter_widgets/test/src/mocks.dart

@@ -1,5 +1,5 @@
 import 'package:mockito/mockito.dart';
-import 'package:stream_chat/stream_chat.dart';
+import 'package:stream_chat_flutter_core/stream_chat_flutter_core.dart';
 
 class MockClient extends Mock implements Client {}