Removing smart card login from my Mac
Use sc_auth unpair …

This worked for me:

/usr/sbin/sc_auth unpair -u [username]


The sc_auth command…


  sc_auth configures a local user account to permit authentication using a supported smart card.  Authentication is via asymmetric key (also known as public-key) encryption.  sc_auth works with signing keys, but not encryption keys.


…with the option unpair:


  unpair   Remove association with a user and keychain. If no specific hash is provided, all associations with a user are removed.