Remove upgrade periodic jobs using boskos (#3866)
Remove upgrade periodic jobs using boskos (#3866)

These jobs have been broken for months. We have decent coverage in our
core testing infra in istio/istio. Any investment would be better spent
improving that, rather than continuing to support these legacy tests
istio/test-infra,istio/test-infra,istio/test-infra,istio/test-infra