chore: Django3 has removed python_2_unicode_compatible.

Execute the codemodes.

openedx/features/course_duration_limits/models.py

@@ -5,14 +5,13 @@ Course Duration Limit Configuration Models
 from django.core.exceptions import ValidationError
 from django.db import models
 from django.utils import timezone
-from django.utils.encoding import python_2_unicode_compatible
+
 from django.utils.translation import ugettext_lazy as _
 
 from openedx.core.djangoapps.config_model_utils.models import StackedConfigurationModel
 from openedx.features.content_type_gating.helpers import correct_modes_for_fbe, enrollment_date_for_fbe
 
 
-@python_2_unicode_compatible
 class CourseDurationLimitConfig(StackedConfigurationModel):
     """
     Configuration to manage the Course Duration Limit facility.