Fixes JS error when sends JingleSessionPC errors to callstats

modules/xmpp/JingleSessionPC.js

             error.source = request.tree();
         }
 
-        // FIXME: JSON.stringify(error) exception for
-        // circular dependancies when we print that error. Maybe we can include
+        // Commented to fix JSON.stringify(error) exception for
+        // circular dependancies when we print that error.
+        // FIXME: Maybe we can include
         // part of the session object
-        error.session = this;
+        // error.session = this;
 
         logger.error("Jingle error", error);
         if (failureCb) {