Allow `ArcanistPhutilLibraryLinter` to run with an out-of-date XHPAST binary
Allow `ArcanistPhutilLibraryLinter` to run with an out-of-date XHPAST binary

Summary: There is no need to check if the XHPAST binary is available here because this linter does not actually parse PHP, it only considers the library map.

Test Plan: Removed the XHPAST binary and ran `arc lint` on a bunch of files.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11528

julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist