LDBDWAuth: fix exceptions for Python 3

src/LDBDWAuth.py

@@ -31,11 +31,10 @@ Grid mapfile authentication and authorisation class.
 # Import.
 import Admin
 import Constants
-import exceptions
 import M2Crypto
 import re
 
-class GridMapError(exceptions.Exception):
+class GridMapError(Exception):
     """
     Raised for errors in GridMap class
     """