removed dead code: getIndexSourceNames was defined twice

lib/python/Products/PluginIndexes/common/UnIndex.py

@@ -382,10 +382,6 @@ class UnIndex(SimpleItem):
         else:
             return 0
 
-    def getIndexSourceNames(self):
-        """ return name of indexed attributes """
-        return (self.id, )
-
     def getIndexSourceNames(self):
         """ return sequence of indexed attributes """
         try: