workflow: provide legacy WorkflowHistoryList for backward compatibility even if WITH_LEGACY_WORKFLOW is False.

in Python 2, _aq_dynamic() returns None without try..except but it raises ValueError in Python 3.

(python 2)
> /SR/parts/erp5/product/ZSQLCatalog/Extensions/zsqlbrain.py(31)_aq_dynamic()
 31  ->   def _aq_dynamic(self, name):
 32         """Acquire an attribute from a real object.
 33         """
 34         if name.startswith('__') :
 35           return None
 36         return getattr(self.getObject(), name, None)
((Pdb)) getattr(self.getObject(), name, None)
*** ValueError: Unable to getObject from ZSQLBrain if ZSQL Method does not retrieve the `path` column from catalog table.
((Pdb)) r
--Return--
> /SR/parts/erp5/product/ZSQLCatalog/Extensions/zsqlbrain.py(36)_aq_dynamic()->None # <-- !!!

One problem with hexdigest is that it's longer and the column was
created as binary(16). We don't have a mechanism to run migrations on
this table, so we use UNHEX in SQL to have the equivalent as digest()
from hexdigest()
Co-authored-by: Jérome Perrin <jerome@nexedi.com>