Eliminate old style import from language tests

tests/language/string_escape3_negative_test.dart

Index: tests/language/string_escape3_negative_test.dart
===================================================================
--- tests/language/string_escape3_negative_test.dart	(revision 15598)
+++ tests/language/string_escape3_negative_test.dart	(working copy)
@@ -1,12 +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.
-
-// Test that newlines cannot be escaped in import tags.
-
-#library('StringEscape3NegativeTest');
-#import('string_escape3_negative_test_helper.dart', prefix: 'foo\
-');
-
-main() {
-}