Minor change to `PhabricatorInfrastructureTestCase::testLibraryMap`

Summary: Modify `PhabricatorInfrastructureTestCase::testLibraryMap` to use `phutil_get_current_library_name()` instead of hard-coding the library name.

Test Plan: See D9844.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9845