Implemented audit.delete notification

In this changeset, I implemented the audit.delete notification.

Partially Implements: blueprint audit-versioned-notifications-api

Change-Id: I8aeb73f4b8d3273d6de7dc9c44674e3041b005ea

watcher/objects/audit.py

@@ -283,3 +283,8 @@ class Audit(base.WatcherPersistentObject, base.WatcherObject,
         self.dbapi.soft_delete_audit(self.uuid)
         self.state = State.DELETED
         self.save()
+
+        def _notify():
+            notifications.audit.send_delete(self._context, self)
+
+        _notify()