Remove Challenge

Author: rcosta358

README.md

@@ -220,23 +220,6 @@ If you get stuck, here are some **hints**:
 
 With the correct implementation, LiquidJava will report an error in line 11 of [StackExample.java](./src/main/java/com/tutorial/part4/exercise/StackExample.java), since we are trying to pop an element of the stack when it is empty.
 
-### 5. Challenge
-
-> Open [Downloader.java](./src/main/java/com/tutorial/part5/Downloader.java). Your task is to refine the `Downloader` class by replacing the `"true"` refinements with the appropriate ones to ensure the correct behavior of the `start`, `updateProgress`, `complete` and `getFile` methods, using the `progress` ghost variable to keep track of the download progress (from `0` to `100`), and the `waiting`, `downloading` and `completed` states.
-
-You will have to use most of the concepts learned throughout this tutorial, including refinement aliases, state refinements, and ghost variables. The following DFA illustrates the allowed state transitions:
-
-![Downloader DFA](./docs/images/downloader_dfa.png)
-
-If you get stuck, here are some **hints**:
-
-- The refinement alias `Percent` should only allow integers between `0` and `100` and then it should be used to refine the `percentage` parameter of the `updateProgress` method
-- You should combine states and ghost variable assertions in the state refinements of the `updateProgress` and `complete` methods using the `&&` operator
-- You should define that the new percentage value in the `updateProgress` method should always be greater than the current `progress` ghost variable value
-- The `getFile` method should only be called when the download is finished
-
-With the correct implementation, LiquidJava should report an error in line 35, since we are trying to complete the download when the progress is not yet 100%. Simply add a new line that updates the progress to 100 before calling the `complete` method to fix the error.
-
 ---
 
 ## Quiz