other deprecated auth features

- Removed PASSWORD() function
- Removed old_passwords variable
- Removed support for
  SET PASSWORD ... = PASSWORD('auth_string')
- Removed support for IDENTIFIED BY PASSWORD clause
- Removed ability to create new user through GRANT
- Removed ability to change user properties such as
  credentials, connection attributes, ssl restriction
  through GRANT
- Removed support for NO_AUTO_CREATE_USER
- Removed --log_builtin_as_identified_by_password
  system variable
- Test changes