Fix analysis issues (flutter#4)

Author: nex3

test/default_test.dart

@@ -81,5 +81,5 @@ void main() {
 /// A wrapper for [neverCalled] that works around sdk#33015.
 void Function() get neverCalledVoid {
   var function = neverCalled;
-  return () => neverCalled();
+  return () => function();
 }

test/stopwatch_test.dart

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import 'dart:async';
-
 import 'package:clock/clock.dart';
 
 import 'package:test/test.dart';