Probably you need to purge cpufrequtils, since it seems to contain
relevant scripts. Keep in mind that systemd-sysv-generator handles init
scripts.
[root@archlinux rocketmouse]# systemd-nspawn -qD /mnt/moonstudio
[root@moonstudio ~]# apt update
[root@moonstudio ~]# apt install cpufrequtils
[root@moonstudio ~]# dpkg -L cpufrequtils | grep init.d/
/etc/init.d/loadcpufreq
/etc/init.d/cpufrequtils
[root@moonstudio ~]# apropos systemd-sysv-generator
systemd-sysv-generator (8) - Unit generator for SysV init scripts
[root@moonstudio ~]# apt purge cpufrequtils libcpufreq0
[root@moonstudio ~]# lsb_release -dc
Description: Ubuntu 16.04.3 LTS
Codename: xenial
I don't know if there are other packages provided by Ubuntu
repositories and/or Mint repositories, but cpufrequtils looks like a
reasonable culprit.