Problem:
=======
The ALWAYS option of the mariadb-binlog --base64-output flag
formats its output incorrectly. This option is deprecated, and
MySQL 8.0 has removed it entirely.

Solution:
========
Adhere to MySQL and remove this option from MariaDB.

Behavioral Changes:
==================
Use Case: ./mariadb-binlog --base64-output
 Previous Behavior: Sets base64-output mode to always
 New Behavior: Error message indicating incomplete argument

Use Case: ./mariadb-binlog --base64-output=always
 Previous Behavior: Sets base64-output mode to always
 New Behavior: Error message indicating invalid argument value

Reviewed By:
==========
Andrei Elkin: <andrei.elkin@mariadb.com>