Temporarily (I hope) remove PHP 5.2 from tests being run on travis-ci

Travis-ci has disabled PHP 5.2. This has happened before when 5.2 didn't compile and then was restored when that was fixed.
See upstream issues:
* #WP31244
* travis-ci/travis-ci#3152
* WP-API/WP-API#846
See #2753

git-svn-id: https://bbpress.svn.wordpress.org/trunk@5616 9866e705-20ec-0310-96e7-cbb4277adcfb

.travis.yml

@@ -9,7 +9,6 @@ language: php
 
 # PHP version used in first build configuration.
 php:
-    - 5.2
     - 5.3
     - 5.4
     - 5.5