[ticket/13454] Remove unused variables

This is part 5 and there is more to come.

PHPBB3-13454

phpBB/phpbb/search/fulltext_native.php

@@ -1733,7 +1733,7 @@ class fulltext_native extends \phpbb\search\base
 	protected function cleanup($text, $allowed_chars = null, $encoding = 'utf-8')
 	{
 		static $conv = array(), $conv_loaded = array();
-		$words = $allow = array();
+		$allow = array();
 
 		// Convert the text to UTF-8
 		$encoding = strtolower($encoding);