Remove old #import, #source, and #library syntax from tests/standalone.

tests/standalone/io/test_extension.dart

Index: tests/standalone/io/test_extension.dart
diff --git a/tests/standalone/io/test_extension.dart b/tests/standalone/io/test_extension.dart
index ad86b9168acaccb18b36607f33f46161ed82a63a..beed87c69a39214affde6cf1bec3d2808cfbf834 100644
--- a/tests/standalone/io/test_extension.dart
+++ b/tests/standalone/io/test_extension.dart
@@ -2,9 +2,9 @@
 // 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("test_extension");
+library test_extension;
 
-#import("dart-ext:test_extension");
+import "dart-ext:test_extension";
 
 class Cat {
   Cat(this.x);