Remove boskos from kubernetes/test-infra

[ixdy]

What should be cleaned up or changed:
I've begun the effort to move boskos into its own repository (https://github.com/kubernetes-sigs/boskos).

I've started tracking this work in kubernetes-sigs/boskos#3. This issue here is mostly an FYI for anyone watching this repo.

Provide any links for context:
kubernetes/org#1783

/area boskos
/assign

[ixdy]

Full removal of the boskos/ directory is blocked by #17719, but basically all of the code is gone now.

/close

[k8s-ci-robot]

@ixdy: Closing this issue.

In response to this:

Full removal of the boskos/ directory is blocked by #17719, but basically all of the code is gone now.

/close

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