Remove unused dart:async imports
As of Dart 2.1, Future/Stream have been exported from dart:core.
diff --git a/pkgs/test_process/lib/test_process.dart b/pkgs/test_process/lib/test_process.dart
index d9dff5d..301ce9d 100644
--- a/pkgs/test_process/lib/test_process.dart
+++ b/pkgs/test_process/lib/test_process.dart
@@ -2,7 +2,6 @@
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
-import 'dart:async';
import 'dart:convert';
import 'dart:io';
