Remove ignored bot_update "force" parameter.

scripts/slave/recipes/dart/dartium.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 12 matching lines @@
   if '-x64-' in builder_name:
     gyp_defines.append('target_arch=x64')
   api.gclient.set_config('dart') # There is no 'dartium' configuration
   s = api.gclient.c.solutions[0]
   s.name = 'src/dart'
   s.url = ('https://chromium.googlesource.com/external/github.com/' +
               'dart-lang/sdk.git')
   s.deps_file = 'tools/deps/dartium.deps/DEPS'
   s.managed = False
   s.revision = api.properties.get('revision')
-  api.bot_update.ensure_checkout(force=True)
+  api.bot_update.ensure_checkout()
 
   api.gclient.runhooks(env={'GYP_GENERATORS': 'ninja',
                             'GYP_DEFINES': ' '.join(gyp_defines)})
   api.gclient.c.got_revision_mapping.pop('src', None)
   api.gclient.c.got_revision_mapping['src/dart'] = 'got_revision'
 
   # gclient api sets Path('[CHECKOUT]') to build/src/dart.  We prefer build/src.
   api.path['checkout'] = api.path['slave_build'].join('src')
 
   with api.step.defer_results():
@@ skipping 27 matching lines @@
       buildername='dartium-linux-x64-dev',
       revision='12345') +
     api.platform('linux', 64))
   yield (
     api.test('dartium-mac-ia32-inc-stable') +
     api.properties.generic(
       mastername='client.dart',
       buildername='dartium-mac-ia32-inc-stable',
       revision='12345') +
     api.platform('mac', 32))