Tests: Fix frontend tests
    
    Test ipatests/test_ipalib/test_frontend.py::test_Command::test_validate fails due to attributes that are no longer present, therefore assertion for these values was removed.
    
    https://fedorahosted.org/freeipa/ticket/5987
    
    Reviewed-By: Ganna Kaihorodova <gkaihoro@redhat.com>