Disable Phortune Paypal payment provider

Summary:
Ref T2787. For test charges, Paypal is putting the charge in a "payment review" state. Dealing with this state requires way more infrastructure than other providers: we're supposed to pause delivery, then poll Paypal every 6 hours to see if the review has resolved.

Since I can't seem to generate normal test charges, I can't test Paypal for now. Disable it until we have more infrastructure.

(This diff gets us further along, up to the point where I hit this issue.)

Test Plan: Read documentation, rolled eyes.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T2787

Differential Revision: https://secure.phabricator.com/D10644