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