feat: remove last cs_comments service references (#37503)

This commit removes all remaining references to cs_comments_service
except the ForumsConfig model. The only purpose of keeping the model
and table around is so that the webapp processes don't start throwing
errors during deployment because they're running the old code for a
few minutes after the database migration has run. We can drop
ForumsConfig and add the drop-table migration after Ulmo is cut.

Also bumps the openedx-forum version to 0.3.7

---------

Co-authored-by: Taimoor  Ahmed <taimoor.ahmed@A006-01711.local>

common/djangoapps/student/tests/test_admin_views.py

@@ -200,7 +200,7 @@ class AdminUserPageTest(TestCase):
 
         Changing the username is still possible using the database or from the model directly.
 
-        However, changing the username might cause issues with the logs and/or the cs_comments_service since it
+        However, changing the username might cause issues with the logs and/or the forum service since it
         stores the username in a different database.
         """
         request = Mock()