Deleting all keychain passwords on MacBook Pro
Keychain Access is built into macOS that stores your passwords, certificates and other sensitive information securely.

You cannot completely delete or disable Keychain Access, but you can delete individual keychains and keys.


Keychain Access
Select the passwords you want to delete
Right mouse click and choose delete




For further use:


You must deselect save password in Keychain (when you get a popup, to enter your password) 
Also don't save passwords in Safari (they are also stored in Keychain)
Third party apps will store you passwords in Keychain. Because it is the safest place on the Mac to store sensitive data like passwords and keys.