R1:7d69d8ae6a0b

Remove support for Balanced payments

Summary: See <https://www.balancedpayments.com/stripe>. Just get rid of support since Phortune is a prototype anyway.

Test Plan: `grep`, poked around Phortune.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: aurelijus, epriestley

Differential Revision: https://secure.phabricator.com/D12074