Our VM SCCM 2012 as been deleted by other administrator the last years and we haven't backup. I want remove all trace of SCCM from our Active directory and workstation but i don't know how to do this.
The only reference to SCCM in Active Directory is the "System Management" container, which only exists if you had created it in the first place; if SCCM is no longer in use, you can safely delete it.
Unfortunately, there is no centralized way to uninstall the SCCM agent from all computers in your environment; you'll need to either perform a manual uninstallation or use some scripting (a startup script assigned via Group Policy could be a good solution). You'll find the relevant documentation here.