remove docgen source and targets from build

pkg/docgen/test/multi_library_code/lib/test_lib.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 test_lib;
-
-import 'test_lib_foo.dart';
-import 'test_lib_bar.dart';
-export 'test_lib_foo.dart';
-export 'test_lib_bar.dart';
-
-/**
- * Doc comment for class [A].
- *
- * Multiline Test
- */
-/*
- * Normal comment for class A.
- */
-class A {
-
-  int _someNumber;
-
-  A() {
-    _someNumber = 12;
-  }
-
-  A.customConstructor();
-
-  /**
-   * Test for linking to parameter [A]
-   */
-  void doThis(int A) {
-    print(A);
-  }
-}
-
-// A trivial use of `B` and `C` to eliminate import warnings
-B sampleMethod(C cInstance) {
-  throw new UnimplementedError();
-}
-
-int positionalDefaultValues([
-    int intConst = 42,
-    bool boolConst = true,
-    List listConst = const [true, 42, 'Shanna', null, 3.14, const []],
-    String stringConst = 'Shanna',
-    Map mapConst = const {'a':1, 2: true, 'c': const [1,null,true]},
-    Map emptyMap = const {},
-    int referencedConst = INT_CONST,
-    ConstClass constructedConstant1 = const ConstClass<int>(0, true),
-    ConstClass constructedConstant2 = const ConstClass(1, false, str: "str")]) {
-  throw new UnimplementedError();
-}
-
-const int INT_CONST = 42;
-
-class ConstClass<T> {
-  final bool boolField;
-  final int intField;
-  final String stringField;
-
-  const ConstClass(this.intField, this.boolField, {String str: 'default'})
-      : this.stringField = str;
-}