Drop usages of Delegating*.typed (dart-lang/stream_channel#50)

pkgs/stream_channel/lib/stream_channel.dart

diff --git a/pkgs/stream_channel/lib/stream_channel.dart b/pkgs/stream_channel/lib/stream_channel.dart
index c806ec6..5693792 100644
--- a/pkgs/stream_channel/lib/stream_channel.dart
+++ b/pkgs/stream_channel/lib/stream_channel.dart
@@ -176,5 +176,5 @@
 
   @override
   StreamChannel<S> cast<S>() => StreamChannel(
-      DelegatingStream.typed(stream), DelegatingStreamSink.typed(sink));
+      stream.cast(), StreamController(sync: true)..stream.cast<T>().pipe(sink));
 }