Request: Delete subscribers

[suelaP]

Short problem description

Currently, the API does not support subscriber removal.

[kniziol]

Does the goal is to create deleteAction() in SubscriberController?

[samtuke]

@kniziol Yes! The implementation is not as simple as deleting the subscriber from the user table. Instead the subscriber can merely be marked as blacklisted, as we should not permanently delete the preferences of a subscriber, particularly if they have opted out from future communications (we must preserve their wish).
Instead the delete procedure for each subscriber should have the same effect as this logic from phpList3: https://github.com/phpList/phplist3/blob/master/public_html/lists/admin/inc/userlib.php#L147