Revert "Fix remaining strong-mode warnings and errors in dart:io."

sdk/lib/io/link.dart

Index: sdk/lib/io/link.dart
diff --git a/sdk/lib/io/link.dart b/sdk/lib/io/link.dart
index 7c937250d7f56e6d08eaaf4ca91cd0c256dc4e4f..25be38c102566f66bb430728647ab8e8ff224485 100644
--- a/sdk/lib/io/link.dart
+++ b/sdk/lib/io/link.dart
@@ -223,7 +223,7 @@ class _Link extends FileSystemEntity implements Link {
     // Atomically changing a link can be done by creating the new link, with
     // a different name, and using the rename() posix call to move it to
     // the old name atomically.
-    return delete().then/*<Link>*/((_) => create(target));
+    return delete().then((_) => create(target));
   }
 
   Future<Link> _delete({bool recursive: false}) {