Revert "Simplify tests under utils/tests to follow StandardTestSuite

utils/tests/import_mapper/test_config.dart

 // 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("import_mapper_test_config");
 
 #import("../../../tools/testing/dart/test_suite.dart");
 
 class ImportMapperTestSuite extends StandardTestSuite {
   ImportMapperTestSuite(Map configuration)
       : super(configuration,
               "import_mapper",
               "utils/tests/import_mapper/src",
               ["utils/tests/import_mapper/import_mapper.status"]);
 
   bool isTestFile(String filename) => filename.endsWith("_tests.dart");
 }