Remove ignored bot_update "force" parameter.

scripts/slave/recipe_modules/chromedriver/example.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.
 
 from recipe_engine import recipe_api
 from recipe_engine.types import freeze
 
 DEPS = [
   'archive',
   'chromedriver',
@@ skipping 24 matching lines @@
 })
 
 def RunSteps(api):
   buildername = api.properties['buildername']
   builder = BUILDERS[buildername]
   android_packages = builder.get('android_packages')
   update_test_log = builder.get('update_test_log')
 
   api.chromium.set_config('chromium')
   api.gclient.set_config('chromium')
-  api.bot_update.ensure_checkout(force=True)
+  api.bot_update.ensure_checkout()
   platform = builder.get('chromedriver_platform')
 
   commit_position = api.commit_position.parse_revision(
       api.properties['got_revision_cp'])
 
   if platform == 'android':
     api.chromedriver.download_prebuilts()
 
   passed = True
   try:
@@ skipping 56 matching lines @@
       api.test('%s_unexpected_prebuilt' % sanitize('Android ChromeDriver')) +
       api.properties.generic(
           buildername='Android ChromeDriver Tests Example',
           slavename='slavename') +
       api.properties(
           parent_build_archive_url='gs://test-domain/test-archive.zip',
           got_revision_cp='refs/heads/master@{#3333333333}') +
       api.step_data(
           'Download Prebuilts.listdir get prebuilt filename',
           api.json.output(['rNone.zip'])))