OOPS DO NOT PUT THOSE FOUR LINES IN THAT FILE. Those four lines are from a non-Debian distribution.
The immediate consequence of adding those four lines: Upon systemctl stop nodm you will get black screen. Nothing you can do will break out. You will have to hit the power button. Let's hope your disks are synced. Upon reboot you had better get those lines back out fast, as every 60 seconds nodm will attempt and fail to start again. Hmmm, perhaps choose recovery mode at the boot menu to avoid nodm trying to start. Now reboot again to finally get everything back to normal.
