[prunerepo] avoid using --repoid for repo listing
    
    On Fedora 26, 'dnf repoquery' throws this error:
    
        dnf: error: argument --repo/--repoid: not allowed with
        argument --disablerepo
    
    Indeed, --repoid seems to be useless when all repositories are
    disabled and only one is enabled (by --repofrompath).