Drop build requirement on zenity
    
    Runtime dependency on zenity was already dropped.
    Dropping on build require as well as the test requiring it is not
    executed while building and we don't ship that test within the built rpms.
    
    Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=2164152
    Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>