budget: do not put budget lines/cells in predicate table for now

What we put in predicate table is not usable yet, so the end result is
same if we put nothing and putting nothing saves us from some
perfomance problems.

bt5/erp5_budget/SkinTemplateItem/portal_skins/erp5_budget/BudgetCell_asPredicate.py

+# We don't have good implementation of budget predicate yet, so don't fill predicate table for now.
+return None
+
 # XXX strict membership is missing ?
 # ideally strict membership should be an option for each category, but this API
 # does not exist in predicates.

bt5/erp5_budget/SkinTemplateItem/portal_skins/erp5_budget/BudgetLine_asPredicate.py

+# We don't have good implementation of budget predicate yet, so don't fill predicate table for now.
+return None
+
+
 context = context.asContext(
              _range_criterion = {'start_date': (context.getStartDateRangeMin(),
                                                 context.getStartDateRangeMax())