calico.md

* calico: add constant calico_min_version_required

and verify current deployed version against it.

* calico: remove upgrade support with data migration

The tool was used pre v3.0.0 and is no longer needed.

* calico: remove old version support from tasks

* calico: remove old ver support from policy ctrl

* calico: remove old ver support from node

* canal: remove old ver support

* remove unused calicoctl download checksums

calico_min_version_required is the oldest version that can be installed
Older versions can be removed.