Bug 761695 - Fix inaccurate commenting. r=peterv

The .wrappedJSObject property only exists when the Xray wrapper subsumes the wrappee.

js/xpconnect/wrappers/WrapperFactory.cpp

@@ -463,9 +463,7 @@ WrapperFactory::Rewrap(JSContext *cx, JSObject *obj, JSObject *wrappedProto, JSO
                      "bad object exposed across origins");
 
         // Cross origin we want to disallow scripting and limit access to
-        // a predefined set of properties. XrayWrapper adds a property
-        // (.wrappedJSObject) which allows bypassing the XrayWrapper, but
-        // we filter out access to that property.
+        // a predefined set of properties.
         XrayType type = GetXrayType(obj);
         if (type == NotXray) {
             wrapper = &FilteringWrapper<CrossCompartmentSecurityWrapper,