Systemd runlevel check not working in debian, ubuntu and archlinux

[marderbot]

https://github.com/CISOfy/lynis/blob/64758216f20bfb198ae45a258fb2bb9e8ecdbc45/include/tests_kernel#L42-L44

The above check doesn't work in:

• Debian 8
• Debian 11
• Ubuntu 20.04
• Archlinux
• Manjaro

Due to that file not being present in them in a default install.

It does work in recent RHEL and Fedora versions.

Using systemctl get-default would be a perfect replacement because if the system uses systemd it must be present unlike the text file.