Replace subscription expired notification

[UweTrottmann]

E.g. wait a day or so before showing it, to avoid confusing users (see below).

Or drop unused code and strings completely.

Issue: billing API might not return current purchase due to error, so the app believes the subscription has expired, even though it has not. E.g. at a later point the billing API will correctly return the purchase.

All based on a few user reports.

Note: currently not showing the notification at all.