Remove unneeded instanceof in test

Author: sea-bass

test/examples/topic-listener.example.js

@@ -47,7 +47,6 @@ describe('Topics Example', function() {
         var expected = messages.slice();
 
         topic.subscribe(function(message) {
-            expect(message).to.be.instanceof(ROSLIB.Message);
             expect(message).to.be.eql(expected.shift());
         });