Remove deprecated packages from pkg directory.

pkg/unmodifiable_collection/lib/unmodifiable_collection.dart

Index: pkg/unmodifiable_collection/lib/unmodifiable_collection.dart
diff --git a/pkg/unmodifiable_collection/lib/unmodifiable_collection.dart b/pkg/unmodifiable_collection/lib/unmodifiable_collection.dart
deleted file mode 100644
index 428bb7d83f0e9ffba0ce88fccfac7ff6e21db140..0000000000000000000000000000000000000000
--- a/pkg/unmodifiable_collection/lib/unmodifiable_collection.dart
+++ /dev/null
@@ -1,23 +0,0 @@
-// Copyright (c) 2013, 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 library used to introduce unmodifiable wrappers for collections.
- *
- * This functionality has been moved to the `collection` library.
- *
- * Please replace the import of this library with:
- *
- *     import "package:collection/wrappers.dart";
- *
- * and change dependencies to match.
- */
-@deprecated
-library unmodifiable_collection;
-
-export "package:collection/wrappers.dart"
-    show UnmodifiableListView,
-         UnmodifiableSetView,
-         UnmodifiableMapView,
-         NonGrowableListView;