Drop unwanted dependencies on chromium_tests recipe module

scripts/slave/recipes/webrtc/ios.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 = [
-  'chromium_tests',
+  'chromium_checkout',
   'depot_tools/bot_update',
   'depot_tools/gclient',
   'ios',
   'recipe_engine/path',
   'recipe_engine/platform',
   'recipe_engine/properties',
   'webrtc'
 ]
 
 
 def RunSteps(api):
   api.gclient.set_config('webrtc_ios')
 
   api.ios.host_info()
 
   checkout_kwargs = {'force': True}
-  checkout_dir = api.chromium_tests.get_checkout_dir({})
+  checkout_dir = api.chromium_checkout.get_checkout_dir({})
   if checkout_dir:
     checkout_kwargs['cwd'] = checkout_dir
   api.bot_update.ensure_checkout(**checkout_kwargs)
 
   build_config_base_dir = api.path['checkout'].join(
       'webrtc',
       'build',
       'ios',
   )
   buildername = api.properties['buildername'].replace(' ', '_')
@@ skipping 201 matching lines @@
           'os': '7.1',
         },
       ],
     })
     + api.step_data(
       'fake tests 1 (fake device iOS 8.0)',
       retcode=2,
     )
   )