The easiest possible way to remove the sccm client is to run the command line ccmsetup.exe /uninstall from windows\ccmsetup folder.
But what if ccmsetup.exe do not exists on some of the client machines and you would require to remove the client on them ? and if ccmsetup.exe does not work for you to remove the sccm client successfully ?
Mike Griswold did a post on this how to do manual executions to remove sccm client without using ccmsetup.exe on the way at his customer place.
So You can perform below steps to manually clean-up all the traces of the client.
1. SMS Agent Host Service
2. CCMSetup service (if present)
3. \windows\ccm directory
4. \windows\ccmsetup directory
5. \windows\ccmcache directory
7. \windows\sms*.mif (if present)
8. HKLM\software\Microsoft\ccm registry keys
9. HKLM\software\Microsoft\CCMSETUP registry keys
10. HKLM\software\Microsoft\SMS registry keys