Drop dependency on hawkey and versioned dependencies on dnf.
    
    These were introduced by commit 48b7c2f9a8b2f220b4adb38a3a41b07700bb6082.
    
    Hawkey is now a dead package (replaced by libdnf).  In any case none
    of the dependencies are now required because the change from
    yumdownloader to dnf download was introduced in Fedora 23, which is
    greater than two Fedora versions ago.