Revert "Reduce API response times by caching migration flag"

This reverts commit 5433af6716.

awx/main/apps.py

@@ -1,17 +1,8 @@
 from django.apps import AppConfig
-from django.db.models.signals import pre_migrate
 from django.utils.translation import ugettext_lazy as _
 
 
-def raise_migration_flag(**kwargs):
-    from awx.main.tasks import set_migration_flag
-    set_migration_flag.delay()
-
-
 class MainConfig(AppConfig):
 
     name = 'awx.main'
     verbose_name = _('Main')
-
-    def ready(self):
-        pre_migrate.connect(raise_migration_flag, sender=self)