Since 248f59e5 (Business Template: Likewise ERP5Site.addERP5Tool(), do
not re-create Tool if it already exists., 2020-06-22) we no longer
update tools, because of the problem that business template does not
currently handle updating objects with lots of sub-objects.

But we realized that we really need to update tools when they contain
configuration as object attributes, like mimetypes_registry, where the
problem was observed.

Instead of unconditionnally skipping any tool during update, we only
skip the ones that were initially managed by ERP5Generator and are moved
to business templates.