spec: add requirement to uucp
    
    Since recently uucp group and user are not created by setup package
    as well as /var/spool/uucp is no longer created by filesystem package
    (#961952). mgetty however still might need those, but we don't want to
    bother with them majority of users. Modem users are quite rare nowadays.
    
    Strictly speaking it is possible to use mgetty without uucp, having
    the package on the system prevents warnings mgetty prints about
    non-existing uucp user and group. Secondly, odds are high that mgetty
    user is also uucp user.