Drop usages of Delegating*.typed (#50)

diff --git a/lib/stream_channel.dart b/lib/stream_channel.dart
index c806ec6..5693792 100644
--- a/lib/stream_channel.dart
+++ b/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));
 }