devserver:  Fix Download call.

The download call no longer takes an async parameter, fix the
call.

Move to python3, Moblab has been using python3 for devserver for some
time.

TEST=stage build on local moblab
BUG=chromium:1143147

Change-Id: If72b637b61ae3d1a6c07722f42dd92f4940ed016
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2505499
Tested-by: Keith Haddow <haddowk@chromium.org>
Auto-Submit: Keith Haddow <haddowk@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
diff --git a/devserver.py b/devserver.py
index f7d6707..23eb4fc 100755
--- a/devserver.py
+++ b/devserver.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 # Copyright (c) 2009-2012 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
@@ -643,8 +643,7 @@
       if clean and os.path.exists(dl.GetBuildDir()):
         _Log('Removing %s' % dl.GetBuildDir())
         shutil.rmtree(dl.GetBuildDir())
-      is_async = kwargs.get('async', False)
-      dl.Download(factory, is_async=is_async)
+      dl.Download(factory)
     finally:
       with DevServerRoot._staging_thread_count_lock:
         DevServerRoot._staging_thread_count -= 1