remove docgen source and targets from build

pkg/docgen/lib/src/models/doc_gen_type.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.models.doc_gen_type;
-
-import '../exports/source_mirrors.dart';
-
-import '../library_helpers.dart';
-
-import 'library.dart';
-import 'mirror_based.dart';
-
-/// Docgen wrapper around the mirror for a return type, and/or its generic
-/// type parameters.
-///
-/// Return types are of a form [outer]<[inner]>.
-/// If there is no [inner] part, [inner] will be an empty list.
-///
-/// For example:
-///        int size()
-///          "return" :
-///            - "outer" : "dart:core.int"
-///              "inner" :
-///
-///        List<String> toList()
-///          "return" :
-///            - "outer" : "dart:core.List"
-///              "inner" :
-///                - "outer" : "dart:core.String"
-///                  "inner" :
-///
-///        Map<String, List<int>>
-///          "return" :
-///            - "outer" : "dart:core.Map"
-///              "inner" :
-///                - "outer" : "dart:core.String"
-///                  "inner" :
-///                - "outer" : "dart:core.List"
-///                  "inner" :
-///                    - "outer" : "dart:core.int"
-///                      "inner" :
-class DocGenType extends MirrorBased {
-  final TypeMirror mirror;
-  final Library owningLibrary;
-
-  DocGenType(this.mirror, this.owningLibrary);
-
-  Map toMap() {
-    var result = getDocgenObject(mirror, owningLibrary);
-    return {
-      // We may encounter types whose corresponding library has not been
-      // processed yet, so look up with the owningLibrary at the last moment.
-      'outer': result.packagePrefix + result.docName,
-      'inner': _createTypeGenerics(mirror).map((e) => e.toMap()).toList(),
-    };
-  }
-
-  /// Returns a list of [DocGenType] objects constructed from TypeMirrors.
-  List<DocGenType> _createTypeGenerics(TypeMirror mirror) {
-    if (mirror is! ClassMirror) return [];
-    return mirror.typeArguments
-        .map((e) => new DocGenType(e, owningLibrary))
-        .toList();
-  }
-}