Fix doc example for let

Made the code sample consistent with the stated output.

Author: djskinner

doc/api/core/operators/let.md

@@ -17,17 +17,6 @@ var obs = Rx.Observable.range(1, 3);
 
 var source = obs.let(function (o) { return o.concat(o); });
 
-var subscription = source.subscribe(
-    function (x) {
-        console.log('Next: ' + x);
-    },
-    function (err) {
-        console.log('Error: ' + err);
-    },
-    function () {
-        console.log('Completed');
-    });
-
 var subscription = source.subscribe(
     function (x) {
         console.log('Next: ' + x);