Prevent raising NotYet in removeIntIdSubscriber

[ale-rt]

Prevent errors on removeIntIdSubscriber when the IKeyReference adapter raises a NotYet, e.g. because the object does not have a proper path.

Some background...

I had to use this patch to migrate a Plone4 site to Plone5.

A couple of examples of object removed triggering the NotYet:

ipdb> IKeyReference(ob, None)
*** NotYet: <SimpleItem at >
ipdb> ob.__dict__
{'_v__object_deleted__': 1, 'isAllowed': True, '__ac_local_roles__': {'admin': ['Owner']}, 'title': 'Generates RSS for folders'}

and:

ipdb> IKeyReference(ob, None)
*** NotYet: 
ipdb> ob.__dict__
{'_real': <Products.CMFCore.DirectoryView.DirectoryView object at 0x7f68fff85410>, '_dirpath': 'Products.CMFPlone:skins/cmf_legacy', '_v__object_deleted__': 1, '_objects': (), '__ac_local_roles__': {'admin': ['Owner']}, 'id': 'cmf_legacy'}

This is a fix similar to 513ca3c