Backport and remove code from the permission app

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

mayan/apps/permissions/managers.py

@@ -3,7 +3,6 @@ from __future__ import unicode_literals
 import logging
 
 from django.db import models
-from django.contrib.contenttypes.models import ContentType
 
 logger = logging.getLogger(__name__)
 
@@ -16,9 +15,3 @@ class RoleManager(models.Manager):
 class StoredPermissionManager(models.Manager):
     def get_by_natural_key(self, namespace, name):
         return self.get(namespace=namespace, name=name)
-
-    def get_for_holder(self, holder):
-        ct = ContentType.objects.get_for_model(holder)
-        return self.model.objects.filter(
-            permissionholder__holder_type=ct
-        ).filter(permissionholder__holder_id=holder.pk)