Revert "Update HTML Purifier to version 4.4.0."

This reverts commit dd205fbad6.

lib/htmlpurifier/library/HTMLPurifier/HTMLModule/Tables.php

@@ -37,9 +37,6 @@ class HTMLPurifier_HTMLModule_Tables extends HTMLPurifier_HTMLModule
                 'abbr'    => 'Text',
                 'colspan' => 'Number',
                 'rowspan' => 'Number',
-                // Apparently, as of HTML5 this attribute only applies
-                // to 'th' elements.
-                'scope'   => 'Enum#row,col,rowgroup,colgroup',
             ),
             $cell_align
         );