chore: Django3 has removed python_2_unicode_compatible.

Execute the codemodes.

openedx/features/announcements/models.py

@@ -4,10 +4,8 @@ Models for Announcements
 
 
 from django.db import models
-from django.utils.encoding import python_2_unicode_compatible
 
 
-@python_2_unicode_compatible
 class Announcement(models.Model):
     """Site-wide announcements to be displayed on the dashboard"""
     class Meta:

openedx/features/content_type_gating/models.py

@@ -5,14 +5,13 @@ Content Type Gating 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 ContentTypeGatingConfig(StackedConfigurationModel):
     """
     A ConfigurationModel used to manage configuration for Content Type Gating (Feature Based Enrollments).

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.

openedx/features/discounts/models.py

@@ -6,13 +6,12 @@ DiscountRestrictionConfig Models
 
 
 from django.db import models
-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
 
 
-@python_2_unicode_compatible
 class DiscountRestrictionConfig(StackedConfigurationModel):
     """
     A ConfigurationModel used to manage restrictons for lms-controlled discounts
@@ -41,7 +40,6 @@ class DiscountRestrictionConfig(StackedConfigurationModel):
         )
 
 
-@python_2_unicode_compatible
 class DiscountPercentageConfig(StackedConfigurationModel):
     """
     A ConfigurationModel to configure the discount percentage for the first purchase discount