Deleted dead link in Docker (#503)

## Describe your PR

Deleted a dead link that used to point to a Haskell dockerized example.


## Checklist

- [x] My PR is related to an opened issue : #494
- [x] I've read the [contributing
guidelines](/CleverCloud/documentation/blob/main/CONTRIBUTING.md)


## Reviewers
_Who should review these changes?_ @CleverCloud/reviewers

content/doc/applications/docker/_index.md

@@ -204,7 +204,6 @@ CMD ["sudo","/root/start.sh"]
 We provide a few examples of dockerized applications on Clever Cloud.
 
 * [Elixir App](https://github.com/CleverCloud/demo-docker-elixir/blob/master/Dockerfile)
-* [Haskell App](https://github.com/CleverCloud/demo-haskell)
 * [Hack / HHVM App](https://github.com/CleverCloud/demo-hhvm)
 * [Seaside / Smalltalk App](https://github.com/CleverCloud/demo-seaside)
 * [Rust App](https://github.com/CleverCloud/demo-rust)