Fix OAuth profile pictures for FB

Summary: Ref T1536. Older versions of this code had a multi-parameter accessor for the data, but this is essentially the only callsite any provider has for that so the new ones don't.

Test Plan: {F46833}

Reviewers: wez, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1536

Differential Revision: https://secure.phabricator.com/D6233