Always give users "fa-user" icons in tokenizers

Summary: Fixes T10247. The flavor icons are unhelpful/confusing in these contexts; show a boringer icon instead.

Test Plan: Used tokenizer to select user with custom profile icon. Reloaded page. Saw boringer icon in both cases.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10247

Differential Revision: https://secure.phabricator.com/D15154