Don't connect Theme.get_active() to post_migrate()

This fixes an IntegrityError when trying to import or load
for the first time another Theme

admin_interface/apps.py

@@ -1,7 +1,6 @@
 # -*- coding: utf-8 -*-
 
 from django.apps import AppConfig
-from django.db.models.signals import post_migrate
 
 
 class AdminInterfaceConfig(AppConfig):
@@ -10,7 +9,5 @@ class AdminInterfaceConfig(AppConfig):
     verbose_name = 'Admin Interface'
 
     def ready(self):
-
+        pass
-        from admin_interface.models import Theme
-        post_migrate.connect(Theme.post_migrate_handler, sender = self)
 

admin_interface/models.py

@@ -12,10 +12,6 @@ from colorfield.fields import ColorField
 @python_2_unicode_compatible
 class Theme(models.Model):
 
-    @staticmethod
-    def post_migrate_handler(sender, **kwargs):
-        Theme.get_active_theme()
-
     @staticmethod
     def post_delete_handler(instance, **kwargs):
         Theme.get_active_theme()