Drop support for ZF2_PATH; update message.

- Zend Framework 2 references are out of date; using an external library location no longer makes sense.

public/index.php

@@ -65,18 +65,8 @@ if (file_exists('vendor/autoload.php')) {
     $loader = include 'vendor/autoload.php';
 }
 
-// Support for ZF2_PATH environment variable
-if ($zf2Path = getenv('ZF2_PATH')) {
-    if (isset($loader)) {
-        $loader->add('Zend', $zf2Path . '/Zend');
-    } else {
-        include $zf2Path . '/Zend/Loader/AutoloaderFactory.php';
-        AutoloaderFactory::factory();
-    }
-}
-
 if (!class_exists('Zend\Loader\AutoloaderFactory')) {
-    throw new RuntimeException('Unable to load ZF2.');
+    throw new RuntimeException('Unable to load Zend Framework autoloader.');
 }
 
 // Run the application!