Simplify tests under utils/tests to follow StandardTestSuite convention.

utils/tests/import_mapper/src/a.dart

Index: utils/tests/import_mapper/src/a.dart
diff --git a/utils/tests/import_mapper/src/a.dart b/utils/tests/import_mapper/src/a.dart
deleted file mode 100644
index 8386f89f7ecafbb47df61c98333653ed407a3f06..0000000000000000000000000000000000000000
--- a/utils/tests/import_mapper/src/a.dart
+++ /dev/null
@@ -1,10 +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.
-
-/** A dummy library for testing import_mapper. */
-#library('a');
-
-#import('b.dart');
-
-main() {}