Disable CertificateRequest in ServerHello in MySQL/MariaDB
You could revoke SSL from the user in one of two ways:

METHOD #1 : Recreate User without REQUIRE SSL

DROP USER IF EXISTS 'username'@'%';
CREATE USER 'username'@'%' IDENTIFIED BY 'passowrd'; 
GRANT ALL ON db_name.* TO 'username'@'%';


METHOD #2 : Hack mysql.user

UPDATE mysql.user SET ssl_type='' WHERE user='username' AND host='%';
FLUSH PRIVILEGES;


CAVEAT

Check release notes on MariaDB concerning METHOD #2.

I think there is a bug doing FLUSH PRIVILEGES; in older versions.

GIVE IT A TRY !!!