Clean up isolate tests.

tests/isolate/isolate_import_negative_test.dart

Index: tests/isolate/isolate_import_negative_test.dart
diff --git a/tests/isolate/isolate_import_negative_test.dart b/tests/isolate/isolate_import_negative_test.dart
deleted file mode 100644
index 1ea91022d8bb00d43e89470c90c5255cc36437b7..0000000000000000000000000000000000000000
--- a/tests/isolate/isolate_import_negative_test.dart
+++ /dev/null
@@ -1,14 +0,0 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// 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.
-
-library IsolateImportNegativeTest;
-// Omitting the following import is an error:
-// import 'dart:isolate';
-
-void entry(msg) {}
-
-main() {
-  Isolate.spawn(entry);
-}
-