fix keyerror in plcorebase.delete
diff --git a/planetstack/core/models/user.py b/planetstack/core/models/user.py
index 1b3be29..8dc87b3 100644
--- a/planetstack/core/models/user.py
+++ b/planetstack/core/models/user.py
@@ -135,6 +135,8 @@
     def delete(self, *args, **kwds):
         # so we have something to give the observer
         purge = kwds.get('purge',False)
+        if purge:
+            del kwds['purge']
         try:
             purge = purge or observer_disabled
         except NameError: