Display principal name while del required principal
    
    Fix is to display the proper principal in error message
    while attempting to delete required principal.
    
    related: https://pagure.io/freeipa/issue/7695
    
    Signed-off-by: Mohammad Rizwan Yusuf <myusuf@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>