[Hub] Free users get card expiry notifications

[JedMeister]

Some Hub users on "free" plans have reported that they are getting "Your card is about to expire" and "your card has expired" warning emails.

Whilst it may be legitimate to send one email notification (perhaps the user would like to keep their card up to date so they can upgrade to a paid plan whenever they want?), sending repeated notifications when it's not neccessary is annoying (as reported and I agree!).

Card issues are noted at the top of the "Plans and Billing" page anyway. So at most, free plan Hub users should get one notification re their card expiry.