It’s still there: https://github.com/discourse/wp-discourse/blob/master/lib/utilities.php#L306
You need to call it with the namespace WPDiscourse\Utilities\Utilities::create_discourse_user( $user )
There is also a sync_sso_record function that would be better to use if you are able to. It takes an array of sso parameters as an argument. You can get them from the get_sso_params function.
I’m in the process of cleaning up this file. I won’t remove any functions that I’ve posted about on meta. If I break anything, let me know.
Edit: I read the OP more closely. I hadn’t realized it was editing the plugin’s code. That part will be broken by the most recent update. It would be better to call either the create_discourse_user or the sync_sso_record function from WPDiscourse\Utilities, and add the my_mm_account_added hook to your functions.php file or a separate plugin.