Make some strings in `ArcanistPhutilXHPASTLinter` translatable

Summary: `pht`ize some string in `ArcanistPhutilXHPASTLinter` so that they are translatable.

Test Plan: Not 100% sure that I am doing it right...

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10431