automate customer removal for S4

[david415]

Automating the customer-cancellation this is a good idea for several reasons; we need this process to ensure our database of customer information is updated when a customer is cancelled. Daira points out that we should keep an accurate historical record of all customers while maintaining a separate cancelled-customer list.

[exarkun]

There are docs for manual cancellation (#448) that can be changed or dropped when this is resolved.

[Liz315]

This appears to be related to #248