Installer: Remove two environmental checks

* envCheckPHP531: Message is outdated ("downgrade to 5.3.0"; the
  current minimum PHP version is 5.3.2), and PHP Bug #50394 has
  not reappeared in any later version.
* envCheckZE1: zend.ze1_compatibility_mode was removed in 5.3.0.

Also updated the error message for envCheckBrokenXML to remove
the "Upgrade to PHP 5.2.9 or later" wording.

Change-Id: Ifc8754151dd23a0314c6739cb78c7ac61a306bc4
Merge "Installer: Remove two environmental checks"