Fix formatted translations in trust plugin
    
    Translation objects have support for format(). This allows to
    get rid of unicode() which has been removed in Python3.
    
    Also some messages to be translated at request time should
    not use format()
    
    Fixes: https://pagure.io/freeipa/issue/7586
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>