[infra] Translate _sources.gypi files to _sources.gni files

sdk/lib/async/async_sources.gypi

Index: sdk/lib/async/async_sources.gypi
diff --git a/sdk/lib/async/async_sources.gypi b/sdk/lib/async/async_sources.gypi
deleted file mode 100644
index 59904c96b808ceed667eaf02c987707237a91a54..0000000000000000000000000000000000000000
--- a/sdk/lib/async/async_sources.gypi
+++ /dev/null
@@ -1,24 +0,0 @@
-# Copyright (c) 2012, 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:async library.
-{
-  'sources': [
-    'async.dart',
-    # The above file needs to be first as it lists the parts below.
-    'async_error.dart',
-    'broadcast_stream_controller.dart',
-    'deferred_load.dart',
-    'future.dart',
-    'future_impl.dart',
-    'schedule_microtask.dart',
-    'stream.dart',
-    'stream_controller.dart',
-    'stream_impl.dart',
-    'stream_pipe.dart',
-    'stream_transformers.dart',
-    'timer.dart',
-    'zone.dart',
-  ],
-}