style(controller): remove extra comma

flake8 doesn't seem to dislike this style, but it looks odd and
does not conform to the rest of the code.

Author: Matthew

controller/api/tests/test_config.py

@@ -540,7 +540,7 @@ def test_unauthorized_user_cannot_modify_config(self):
                                     HTTP_AUTHORIZATION='token {}'.format(unauthorized_token))
         self.assertEqual(response.status_code, 403)
 
-    def _test_app_healthcheck(self,):
+    def _test_app_healthcheck(self):
         # post a new build, expecting it to pass as usual
         url = "/v1/apps/{self.app}/builds".format(**locals())
         body = {'image': 'autotest/example'}