On Zope2, python scripts do not have __code__, they only have
func_code (and same for __defauls__/func_defaults).
We tried to backport the support of __code__ from Zope4 as a Zope2
patch - it was SlapOS patch 4fa33dfc6 (erp5: py3: `func_{code,defaults}`
was replaced in Python3 by `__{code,defaults}__`., 2022-04-25),
but this patch was incomplete. We tried to backport more, but then
realized that we don't need to use __code__ on ERP5 master yet,
because ERP5 master branch is still supporting Zope2 only.

This patch revert a small part of a17bb910 (py2/py3: Make Products
code compatible with both python2 and python3., 2022-04-13), the part
where we use f.__code__ where f might be a python script. For now,
we'll apply this patch only on the Zope4 branch.

A few places where f.func_code was used and f was a for sure not a
python script but a simple class method or function are kept here, as
__code__ support is missing only on in ZODB scripts.