removing text string from class*.php file

I am customizing our customer emails.
I have had success with the php files in woocommerce/templates. I just created a woocommerce directory in my child theme and everything is good.
However, I am trying to modify the order received email the customer receives and remove the line of text that says “Thanks for using {our website}”
I have found the text string in -wp-content\plugins\woocommerce\includes\emails\class-wc-email-customer-processing-order.php
I can of course modify this file but when I update WC I will lose my changes. How do I update/modify these files and have them last through an update?

TLDR;

I want to remove:
public function get_default_additional_content() {
return __( ‘Thanks for using {site_address}!’, ‘woocommerce’ );
}

from class-wc-email-customer-processing-order.php

I tried using:
remove_action(‘Thanks for using {site_address}!’, ‘woocommerce’);
that did not work.