This commit changes the behavior of the optin checkbox that MailPoet
adds to the WooCommerce checkout.
Now the checkbox is not checked by default for logged in users who
already subscribed to a list. Also, users won't be unsubscribed anymore
and have their global status change to unsubscribed if they uncheck the
checkbox.
The only action that is performed after this change is to subscribe
users if they check the checkbox.
This change was implemented both for the normal checkout and the block
checkout.
It was also necessary to remove the AutomateWoo integration that
depended on subscribers being unsubscribed during checkout.
[MAILPOET-4178]
