Remove package:unittest from some tests

tests/lib/async/stream_periodic5_test.dart

Index: tests/lib/async/stream_periodic5_test.dart
diff --git a/tests/lib/async/stream_periodic5_test.dart b/tests/lib/async/stream_periodic5_test.dart
index 46b685c53bc7cb356b21c3476fc4141c34e88e11..8ab0665d593b0c603cadfdd0d28b66e40892a289 100644
--- a/tests/lib/async/stream_periodic5_test.dart
+++ b/tests/lib/async/stream_periodic5_test.dart
@@ -6,7 +6,7 @@
 library dart.test.stream_from_iterable;
 
 import "dart:async";
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 watchMs(Stopwatch watch) {
   int microsecs = watch.elapsedMicroseconds;
@@ -38,7 +38,7 @@ main() {
           watch.start();
           subscription.resume();
         });
-      } 
+      }
     }, onDone: expectAsync(() { }));
   });
 }