Revert "erp5_core: Fix unicode bug on ZODB History view."

This reverts commit 40fded3e.

It is not good to mix unicode and str for UI. Use utf8 str only.

product/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_core/Base_getZODBHistoryList.py

@@ -13,7 +13,7 @@ def beautifyChange(change_dict):
   for property_name, property_value in sorted(change_dict.items()):
     if isinstance(property_value, six.binary_type):
       try:
-        property_value = six.text_type(property_value, 'utf-8')
+        six.text_type(property_value, 'utf-8')
       except UnicodeDecodeError:
         property_value = '(binary)'
     change_list.append('%s:%s' % (property_name, property_value))