Move libsemanage from post requires to requires

libsemanage owns /etc/selinux, and since our package maintains files under there we depend on that directory and thus libsemanage

unfortunately we cannot get rid of libsemanage easily anyway because shadow-utils depends on it as well (probably for useradd -Z).
compiling shadow-utils without --use-selinux might be a bad idea though since that will also exclude libselinux.