storage: use delete() method on model instead of post_delete signal

circle/storage/models.py

@@ -4,7 +4,6 @@ import logging
 import uuid
 
 from django.db import models
-from django.db.models.signals import post_delete
 from django.utils.translation import ugettext_lazy as _
 from model_utils.models import TimeStampedModel
 from sizefield.models import FileSizeField
@@ -145,10 +144,7 @@ class Disk(TimeStampedModel):
         self.save()
         return True
 
-    @classmethod
-    def delete_signal(cls, sender, instance, using, **kwargs):
+    def delete(self):
         # TODO
         # StorageDriver.delete_disk.delay(instance.to_json()).get()
         pass
-
-post_delete.connect(Disk.delete_signal, sender=Disk)