index/reindex/unindex the object itself

Do not defer to p.a.discussion own tool.

That's needed so that collective.indexing can patch comments,
so in turn can be indexed by Solr.

plone/app/discussion/subscribers.py

@@ -5,12 +5,10 @@ from Products.CMFCore.utils import getToolByName
 def index_object(obj, event):
     """Index the object when it is added/modified to the conversation.
     """
-    catalog = getToolByName(obj, 'portal_catalog')
-    return catalog.reindexObject(obj)
+    obj.indexObject()
 
 
 def unindex_object(obj, event):
     """Unindex the object when it is removed from the conversation.
     """
-    catalog = getToolByName(obj, 'portal_catalog')
-    return catalog.unindexObject(obj)
+    obj.unindexObject()