Remove deprecated parts of dart:async.

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 2a8bfdcdc28b73d050730d7c13216f2be5d68d0a..0aa741258d8723afe76333fbc14f79d832d85a44 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -221,6 +221,7 @@ scheduled_test/test/scheduled_test/timeout_test: Fail # http://dartbug.com/8440
 scheduled_test/test/scheduled_test/wrap_async_test: Fail # http://dartbug.com/8440
 scheduled_test/test/scheduled_test/wrap_future_test: Fail # http://dartbug.com/8440
 
+
 */test/analyzer_test: Skip  # No need to run analysis tests on browser bots
 
 # Skip tests on the browser if the test depends on dart:io
@@ -383,3 +384,7 @@ unittest/test/mock_test: StaticWarning
 watcher/test/directory_watcher_test: StaticWarning
 watcher/test/no_subscription_test: StaticWarning
 watcher/test/ready_test: StaticWarning
+
+[ $runtime == vm ]
+# Issue surfaced after removing deprecated async features.
+scheduled_test/test/scheduled_test/nested_task_test: RuntimeError