rfac: remove asset package

packages/stream_chat_v1/lib/pinned_messages_screen.dart

@@ -221,12 +221,4 @@ class _PinnedMessagesScreenState extends State<PinnedMessagesScreen> {
       c!.dispose();
     }
   }
-}
-
-class _AssetPackage {
-  Attachment attachment;
-  Message message;
-  VideoPlayerController? videoPlayer;
-
-  _AssetPackage(this.attachment, this.message, this.videoPlayer);
-}
+}