Why remove:
* For self-hosters, payment-related features are unused and dead weight
* For SaaS (any would-be Healthchecks.io competitors), the existing
payment handling logic is not very useful either, as it would need to
be heavily modified to match their business model, pricing, chosen
payment gateway
* For the hosted service (Healthchecks.io), the up-to-date billing code
lives in a private fork of this repo. Maintenance is easier if this
repo does not have an older, diverging version of the same
functionality
A few payment-related bits are staying at least for time being:
* the "USE_PAYMENTS" setting
* the hc.payments.models.Subscription model
* tiny stubs for the "Pricing" and "Billing" pages
They are used in various places in the code and templates,
and I think ripping them out in one go would be too disruptive.
