Remove ignored bot_update "force" parameter.

scripts/slave/recipes/dart/dart2js.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 DEPS = [
   'depot_tools/bot_update',
   'depot_tools/gclient',
   'file',
   'recipe_engine/path',
   'recipe_engine/platform',
@@ skipping 58 matching lines @@
     options_end = - 3
   except ValueError:
     sharded = False
     options_end = - 1
   options = builder_fragments[3:options_end]
   for option in options:
     assert all_options.has_key(option)
 
   api.gclient.set_config('dart')
   api.path.c.dynamic_paths['tools'] = None
-  api.bot_update.ensure_checkout(force=True)
+  api.bot_update.ensure_checkout()
   api.path['tools'] = api.path['checkout'].join('tools')
 
   api.gclient.runhooks()
 
   api.python('taskkill before building',
              api.path['checkout'].join('tools', 'task_kill.py'),
              args=['--kill_browsers=True'],
              cwd=api.path['checkout'])
 
   # If we ever build debug mode, use target dart2js_bot_debug, which skips try.
@@ skipping 96 matching lines @@
       api.properties.generic(mastername='client.dart',
           buildername='dart2js-linux-jsshell-hostchecked-csp-3-5-be'))
    yield (
       api.test('dart2js-win7-ie10-dev') + api.platform('win', 32) +
       api.properties.generic(mastername='client.dart',
                              buildername='dart2js-win7-ie10-dev'))
    yield (
       api.test('dart2js-linux-drt-be') + api.platform('linux', 64) +
       api.properties.generic(mastername='client.dart',
                              buildername='dart2js-linux-drt-93-105-dev'))