ERP5{,Type.Core}.InteractionWorkflow: Deprecate activeScript.

Replace it with a method on ERP5Type.Base so these activities get found
by CopySupport.unindexObject and flushed, rather than remaining on the
interaction workflow's context and failing when run.
It seems a lot more likely for a document to be deleted while interactions
are being spawned than an interaction workflow itself. So this should be
a net benefit in activity stability.