When a Phortune subscription has a removed payment method, be more explicit about it

Summary:
Currently, when a payment method is invalid we still render the full name and let you save the form without making changes. This can be confusing.

Instead:

• Render "<Deleted Payment Method>", literally.
• Render an error immediately.
• Prevent the form from being saved without changing the method.

Test Plan: {F1955487}

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D16935