Simplify tests under utils/tests to follow StandardTestSuite convention.

utils/tests/import_mapper/src/import_mapper_tests.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_tests');
-
-#import('../../../import_mapper/import_mapper.dart', prefix: 'mapper');
-
-// TODO(rnystrom): Better path to unittest.
-#import('../../../../lib/unittest/unittest_vm.dart');
-
-main() {
-  group('generateImportMap', () {
-    test('walks import graph', () {
-      final expected = { 'b.dart': 'b.dart', 'c.dart': 'c.dart' };
-      final actual = mapper.generateImportMap(
-          'utils/tests/import_mapper/src/c.dart',
-          (context, name) => name);
-      expect(actual).equals(expected);
-    });
-  });
-}