appropriating Shailen's excellent Futures intro into tutorial

src/site/articles/using-future-based-apis/code/example4.dart

Index: src/site/articles/using-future-based-apis/code/example4.dart
diff --git a/src/site/articles/using-future-based-apis/code/example4.dart b/src/site/articles/using-future-based-apis/code/example4.dart
deleted file mode 100644
index 80af6af932e91bba348a35597f072bad394b9ee1..0000000000000000000000000000000000000000
--- a/src/site/articles/using-future-based-apis/code/example4.dart
+++ /dev/null
@@ -1,16 +0,0 @@
-import 'dart:io';
-import 'dart:async';
-
-void main() {
-  expensiveA().then((aValue) => expensiveB()) 
-              .then((bValue) => expensiveC()) 
-              .then((cValue) => doSomethingWith(cValue));
-}
-
-Future expensiveA() => new Future.value('from expensiveA');
-Future expensiveB() => new Future.value('from expensiveB');
-Future expensiveC() => new Future.value('from expensiveC');
-
-doSomethingWith(value) {
-  print(value);
-}