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