Remove dart:platform library.

sdk/lib/platform/platform_sources.gypi

Index: sdk/lib/platform/platform_sources.gypi
diff --git a/sdk/lib/platform/platform_sources.gypi b/sdk/lib/platform/platform_sources.gypi
deleted file mode 100644
index 6bca2b3f4d65111dccc91af968754d9c97f34673..0000000000000000000000000000000000000000
--- a/sdk/lib/platform/platform_sources.gypi
+++ /dev/null
@@ -1,11 +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 file contains all sources for the dart:platform library.
-{
-  'sources': [
-    'platform.dart',
-    # The above file needs to be first as it lists the parts below.
-  ],
-}