remove docgen source and targets from build

pkg/docgen/test/multi_library_code/lib/test_lib2_foo.dart

Index: pkg/docgen/test/multi_library_code/lib/test_lib2_foo.dart
diff --git a/pkg/docgen/test/multi_library_code/lib/test_lib2_foo.dart b/pkg/docgen/test/multi_library_code/lib/test_lib2_foo.dart
deleted file mode 100644
index 1b3d037c5bce3add4829e93b527bc5eb7f01f821..0000000000000000000000000000000000000000
--- a/pkg/docgen/test/multi_library_code/lib/test_lib2_foo.dart
+++ /dev/null
@@ -1,15 +0,0 @@
-// 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_lib2_foo;
-
-export 'test_lib2_bar.dart';
-
-class Foo {
-
-}
-
-main() {
-  print('hello world');
-}