remove docgen source and targets from build

pkg/docgen/lib/src/io.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.
-
-/// This is a helper library to make working with io easier.
-library docgen.io;
-
-// TODO(janicejl): listDir, canonicalize, resolveLink, and linkExists are from
-// pub/lib/src/io.dart. If the io.dart file becomes a package, should remove
-// copy of the functions.
-
-import 'dart:io';
-import 'package:path/path.dart' as path;
-
-/// Lists the contents of [dir].
-///
-/// If [recursive] is `true`, lists subdirectory contents (defaults to `false`).
-///
-/// Excludes files and directories beginning with `.`
-///
-/// The returned paths are guaranteed to begin with [dir].
-List<String> listDir(String dir, {bool recursive: false,
-  List<FileSystemEntity> listDir(Directory dir)}) {
-  if (listDir == null) listDir = (Directory dir) => dir.listSync();
-
-  return _doList(dir, new Set<String>(), recursive, listDir);
-}
-
-List<String> _doList(String dir, Set<String> listedDirectories, bool recurse,
-    List<FileSystemEntity> listDir(Directory dir)) {
-  var contents = <String>[];
-
-  // Avoid recursive symlinks.
-  var resolvedPath = new Directory(dir).resolveSymbolicLinksSync();
-  if (listedDirectories.contains(resolvedPath)) return [];
-
-  listedDirectories = new Set<String>.from(listedDirectories);
-  listedDirectories.add(resolvedPath);
-
-  var children = <String>[];
-  for (var entity in listDir(new Directory(dir))) {
-    // Skip hidden files and directories
-    if (path.basename(entity.path).startsWith('.')) {
-      continue;
-    }
-
-    contents.add(entity.path);
-    if (entity is Directory) {
-      // TODO(nweiz): don't manually recurse once issue 4794 is fixed.
-      // Note that once we remove the manual recursion, we'll need to
-      // explicitly filter out files in hidden directories.
-      if (recurse) {
-        children.addAll(_doList(entity.path, listedDirectories, recurse,
-            listDir));
-      }
-    }
-  }
-
-  contents.addAll(children);
-  return contents;
-}