Remove kindnet assets and tests from downstream repo

[ggiguash]

Note that kindnet was added downstream from release-4.19 onwards.
Flannel CNI should be removed from release-4.18.

See USHIFT-6216

[ggiguash]

The following PRs are implementing the change downstream:

• USHIFT-6216: Remove kindnet and kube-proxy from MicroShift downstream repo openshift/microshift#5608
• [release-4.20] USHIFT-6216: Remove kindnet and kube-proxy from MicroShift downstream repo openshift/microshift#5610
• [release-4.19] USHIFT-6216: Remove kindnet and kube-proxy from MicroShift downstream repo openshift/microshift#5611
• [release-4.18] USHIFT-6216: Remove flannel and kube-proxy from MicroShift downstream repo openshift/microshift#5609

[ggiguash]

All the downstream PRs merged. Closing the current issue as complete.