remove docgen source and targets from build

pkg/docgen/test/multi_library_code/lib/test_lib2.dart

Index: pkg/docgen/test/multi_library_code/lib/test_lib2.dart
diff --git a/pkg/docgen/test/multi_library_code/lib/test_lib2.dart b/pkg/docgen/test/multi_library_code/lib/test_lib2.dart
deleted file mode 100644
index b28f6d89f9f6a1177f8abdd27acd7169a389ea91..0000000000000000000000000000000000000000
--- a/pkg/docgen/test/multi_library_code/lib/test_lib2.dart
+++ /dev/null
@@ -1,9 +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;
-
-export 'test_lib2_foo.dart';
-
-String fooFunc(bool fooFuncParam(int x)) => 'hi';