refactor: update user instance serialization in user_group.py for improved clarity

Author: wxg0103

apps/users/serializers/user_group.py

@@ -240,7 +240,6 @@ def page(self, current_page, page_size):
                     "id": str(relation.user.id),
                     "username": relation.user.username,
                     "nick_name": relation.user.nick_name,
-                    "email": relation.user.email,
                     "system_user_group_relation_id": str(relation.id),
                 },
             )