function desactiva_email_bienvenida() {
 //Remove original use created emails
 remove_action( 'register_new_user', 'wp_send_new_user_notifications' );
 remove_action( 'edit_user_created_user', 'wp_send_new_user_notifications', 10, 2 );
 
}

add_action( 'init', 'desactiva_email_bienvenida' );