xmlrpc3: remove missing arguments

ex is not defined in this context, remove it and just log an error
that the cleanup failed.

Common/bkr/common/xmlrpc3.py

@@ -356,7 +356,7 @@ def _kerberos_verify_response(vc, host, handler, headers):
         rc = kerberos.authGSSClientClean(vc)
         if rc != 1:
             errcode = 401
-            errmsg = "KERBEROS: Could not clean-up GSSAPI: %s/%s" % (ex[0][0], ex[1][0])
+            errmsg = "KERBEROS: Could not clean-up GSSAPI"
             raise xmlrpclib.ProtocolError(host + handler, errcode, errmsg, headers)
 
     def single_request(self, host, handler, request_body, verbose=0):