Move email_marketing startup.py to AppConfig::ready().

Remove query counting of LMS signals.

lms/djangoapps/email_marketing/apps.py

+"""
+Configuration for the email_marketing Django application.
+"""
+from django.apps import AppConfig
+
+
+class EmailMarketingConfig(AppConfig):
+    """
+    Configuration class for the email_marketing Django application.
+    """
+    name = 'email_marketing'
+    verbose_name = "Email Marketing"
+
+    def ready(self):
+        # Register the signal handlers.
+        from . import signals  # pylint: disable=unused-import

lms/djangoapps/email_marketing/startup.py

-""" email_marketing app. """
-# this is here to support registering the signals in signals.py
-from email_marketing import signals  # pylint: disable=unused-import

lms/envs/common.py

@@ -2289,7 +2289,7 @@ INSTALLED_APPS = [
     'django_sites_extensions',
 
     # Email marketing integration
-    'email_marketing',
+    'email_marketing.apps.EmailMarketingConfig',
 
     # additional release utilities to ease automation
     'release_util',

openedx/core/djangoapps/lang_pref/tests/test_middleware.py

@@ -231,14 +231,7 @@ class TestUserPreferenceMiddleware(TestCase):
         # No preference yet, should write to the database
 
         self.assertEqual(get_user_preference(self.user, LANGUAGE_KEY), None)
-
-        # The 'email_marketing' app is installed in the LMS env but not the CMS env. It listens for the
-        # USER_FIELD_CHANGED signal (utils.model_utils) and does a query to check the EmailMarketingConfiguration
-        # table to see if Sailthru integreation is enabled.
-        expected_queries = 6 if 'email_marketing' in settings.INSTALLED_APPS else 5
-        with self.assertNumQueries(expected_queries):
-            self.middleware.process_request(self.request)
-
+        self.middleware.process_request(self.request)
         self.assertEqual(get_user_preference(self.user, LANGUAGE_KEY), 'es')
 
         response = mock.Mock(spec=HttpResponse)
@@ -261,14 +254,7 @@ class TestUserPreferenceMiddleware(TestCase):
         # Cookie changed, should write to the database again
 
         self.request.COOKIES[settings.LANGUAGE_COOKIE] = 'en'
-
-        # The 'email_marketing' app is installed in the LMS env but not the CMS env. It listens for the
-        # USER_FIELD_CHANGED signal (utils.model_utils) and does a query to check the EmailMarketingConfiguration
-        # table to see if Sailthru integreation is enabled.
-        expected_queries = 6 if 'email_marketing' in settings.INSTALLED_APPS else 5
-        with self.assertNumQueries(expected_queries):
-            self.middleware.process_request(self.request)
-
+        self.middleware.process_request(self.request)
         self.assertEqual(get_user_preference(self.user, LANGUAGE_KEY), 'en')
 
         with self.assertNumQueries(1):