removed a broken link (#7251)

Co-authored-by: manigandan <[email protected]>

Author: iamurmani

more/free-programming-playgrounds.md

@@ -100,7 +100,6 @@
 
 ### Docker
 
-* [Katakoda](https://www.katacoda.com/courses/docker/playground)
 * [Play with Docker](https://labs.play-with-docker.com)
 
 
@@ -192,7 +191,6 @@
 
 ### Kubernetes
 
-* [Katakoda](https://www.katacoda.com/courses/kubernetes/playground)
 * [Play with Kubernetes](https://labs.play-with-k8s.com)