Update library map for phutil_is_utf8_slowly.

Summary: It appears that arc liberate wasn't run for D9472.

Test Plan: Meh...

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9665