Update free-courses-en.md (EbookFoundation#6887)

The resource has been removed

Author: pouliose

Diff for: courses/free-courses-en.md

@@ -385,7 +385,6 @@
 * [Docker Tutorial for Beginners](https://www.youtube.com/watch?v=fqMOX6JJhGo) - FreeCodeCamp
 * [Docker Tutorial Videos \| DevOps Tool](https://www.youtube.com/playlist?list=PL9ooVrP1hQOHUKuqGuiWLQoJ-LD25KxI5) - edureka!
 * [IIEC RISE 1.0 Docker](https://www.youtube.com/playlist?list=PLAi9X1uG6jZ30QGz7FZ55A27jPeY8EwkE)
-* [Learn Docker, Container Runtimes, Builders and Registries](https://www.katacoda.com/courses/container-runtimes) - Katacoda
 
 
 ### Flutter