Crashtest fix follow up from bug 399227 - Add missing removeAttribute to let the crashtests finish

layout/xul/base/src/tree/src/crashtests/399227-1.xul

@@ -14,6 +14,8 @@
     selection.select(0);
     tree.parentNode.removeChild(tree);
     selection.rangedSelect(1, 1, false);
+
+    document.documentElement.removeAttribute("class");
   }
   </script>
 

layout/xul/base/src/tree/src/crashtests/399227-2.xul

@@ -17,6 +17,8 @@
     selection.currentColumn = treecolumn0;
     tree.parentNode.removeChild(tree);
     selection.currentColumn = treecolumn1;
+
+    document.documentElement.removeAttribute("class");
   }
   </script>