How to stop OS X 10.11.6 (El Capitan) from using keychain
You can remove all passwords stored in Keychain via menu File -> Delete Keychain "login". This will create a 'fresh' keychain; you only have to remember not to store any new passwords in it when the system asks for it.





For Safari, open its Preferences and go to the Passwords tab. Uncheck the 'AutoFill user names and passwords' option: