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

sdk/lib/isolate/isolate_sources.gypi

Index: sdk/lib/isolate/isolate_sources.gypi
diff --git a/sdk/lib/isolate/isolate_sources.gypi b/sdk/lib/isolate/isolate_sources.gypi
deleted file mode 100644
index 8d3ff849673678ce3d2fd7b7d5d00d1dd1f23c89..0000000000000000000000000000000000000000
--- a/sdk/lib/isolate/isolate_sources.gypi
+++ /dev/null
@@ -1,11 +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.
-
-{
-  'sources': [
-    'isolate.dart',
-    # The above file needs to be first as it lists the parts below.
-    'capability.dart',
-  ],
-}