docs(e2e): Update kube version in e2e docs
docs(e2e): Update kube version in e2e docs

This PR is to update the default version to 1.19 if K8S_VERSION in not
passed, as well as to remove old versions that cilium is no longer
supported.

Signed-off-by: Tam Mach <928487046a9c42ed56ed508a413e2eaabffae612@yahoo.com>

cilium/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,cilium-team/cilium,michi-covalent/cilium,cilium-team/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium