Drop k3s as a learning environment

"K3s is a highly available, certified Kubernetes distribution designed
for production workloads in unattended, resource-constrained, remote
locations or inside IoT appliances"

The product's own web page doesn't mention using it for learning.

Author: Tim Bannister

content/en/docs/setup/_index.md

@@ -46,7 +46,6 @@ If you're learning Kubernetes, use the Docker-based solutions: tools supported b
 |                     | [MicroK8s](https://microk8s.io/)|
 |                     | [IBM Cloud Private-CE (Community Edition)](https://github.com/IBM/deploy-ibm-cloud-private) |
 |                     | [IBM Cloud Private-CE (Community Edition) on Linux Containers](https://github.com/HSBawa/icp-ce-on-linux-containers)|
-|                     | [k3s](https://k3s.io)|
 
 
 ## Production environment