remove docgen source and targets from build

pkg/docgen/test/only_lib_content_in_pkg_test.dart

-// Copyright (c) 2014, 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 docgen.test.only_lib_content_in_pkg;
-
-import 'dart:io';
-
-import 'package:path/path.dart' as p;
-import 'package:scheduled_test/descriptor.dart' as d;
-import 'package:scheduled_test/scheduled_test.dart';
-
-import '../lib/docgen.dart' as dg;
-import 'util.dart';
-
-void main() {
-
-  setUp(() {
-    scheduleTempDir();
-  });
-
-  test('exclude non-lib code from package docs', () {
-    schedule(() {
-      var thisScript = Platform.script;
-      var thisPath = p.fromUri(thisScript);
-      expect(p.basename(thisPath), 'only_lib_content_in_pkg_test.dart');
-      expect(p.dirname(thisPath), endsWith('test'));
-
-      var packageRoot = Platform.packageRoot;
-      if (packageRoot == '') packageRoot = null;
-
-      var codeDir = p.normalize(p.join(thisPath, '..', '..'));
-      expect(FileSystemEntity.isDirectorySync(codeDir), isTrue);
-      return dg.docgen(['$codeDir/'], out: p.join(d.defaultRoot, 'docs'),
-          packageRoot: packageRoot);
-    });
-
-    d.dir('docs', [
-        d.dir('docgen', [
-          d.matcherFile('docgen.json',  isJsonMap)
-        ]),
-        d.matcherFile('index.json', isJsonMap),
-        d.matcherFile('index.txt', hasSortedLines),
-        d.matcherFile('library_list.json', isJsonMap),
-        d.nothing('test_lib.json'),
-        d.nothing('test_lib-bar.json'),
-        d.nothing('test_lib-foo.json')
-    ]).validate();
-
-  });
-}