Move the purge permission logic to the manager

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/permissions/management/commands/purgepermissions.py

@@ -2,7 +2,6 @@ from __future__ import unicode_literals
 
 from django.core.management.base import BaseCommand
 
-from ...classes import Permission
 from ...models import StoredPermission
 
 
@@ -10,11 +9,4 @@ class Command(BaseCommand):
     help = 'Remove obsolete permissions from the database'
 
     def handle(self, *args, **options):
-        for permission in StoredPermission.objects.all():
-            try:
-                Permission.get(
-                    pk='{}.{}'.format(permission.namespace, permission.name),
-                    proxy_only=True
-                )
-            except KeyError:
-                permission.delete()
+        StoredPermission.objects.purge_obsolete()