How do I remove the proprietary AMD ATI Radeon fglrx drivers from Linux Mint Debian Cinnamon System?

Try to completely remove your AMD ATI RADEON drivers from your Linux Mint Debian system:
sudo apt-get purge "fglrx.*"

Remove your xorg.conf
sudo rm /etc/X11/xorg.conf

Reinstall xorg completely
sudo apt-get install --reinstall xserver-xorg-core libgl1-mesa-glx:i386 libgl1-mesa-dri:i386 libgl1-mesa-glx:amd64 libgl1-mesa-dri:amd64

Re-configure Xorg
sudo dpkg-reconfigure xserver-xorg

Reboot
sudo reboot

You should be greeted with lightdm, this will default everything x the same way a fresh install would.