Make PHP echo tags always available

Summary: As of PHP 5.4, PHP echo tags (<?=) are always available, regardless of the short_open_tag INI setting. See http://php.net/manual/en/language.basic-syntax.phptags.php.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14004