Flip GN bots to be purely driven by //testing/buildbot/*.json files for tests.

scripts/slave/recipe_modules/chromium/api.py

Index: scripts/slave/recipe_modules/chromium/api.py
diff --git a/scripts/slave/recipe_modules/chromium/api.py b/scripts/slave/recipe_modules/chromium/api.py
index 81c4887232727e3b90bd1a71f1bb8c19728f31b8..caea92bccf1bb4e179b7b1eadb39eec46316421d 100644
--- a/scripts/slave/recipe_modules/chromium/api.py
+++ b/scripts/slave/recipe_modules/chromium/api.py
@@ -604,20 +604,6 @@ class ChromiumApi(recipe_api.RecipeApi):
                   script=self.m.path['checkout'].join('tools', 'mb', 'mb.py'),
                   args=args)
 
-  def run_gn_check(self):
-    # TODO(dpranke): Figure out if we should use the '_x64' thing to
-    # consistent w/ GYP, or drop it to be consistent w/ the other platforms.
-    build_dir = '//out/%s' % self.c.build_config_fs
-
-    self.m.python(
-        name='gn check',
-        script=self.m.path['depot_tools'].join('gn.py'),
-        args=[
-            '--root=%s' % str(self.m.path['checkout']),
-            'check',
-            build_dir,
-        ])
-
   def taskkill(self):
     self.m.python(
       'taskkill',