Revert "Folder: change syntax for base classes"

This reverts commit 77286e35.

SyntaxError on py2
3 jobs for zope4py3 in 0 seconds
Status Job ID Name Coverage
  External
failed ERP5.CodingStyleTest-Zope4Py3

01:36:44

failed ERP5.UnitTest-Zope4Py3

01:19:26

failed ERP5.UnitTest-Zope4Py3-Py2

01:27:26