Remove knative/build options/dependencies from prow

[vdemeester]

What should be cleaned up or changed:

Knative build (knative/build) is now deprecated and read-only, hence not maintained anymore — see knative/build#614 for the history.

Prow shouldn't rely on it as it is not maintained anymore, and should focus on tektoncd/pipeline instead (which is kinda already the case as it is also supported in Prow).

Additionnaly, this would remove github.com/knative/* dependencies as knative/build didn't switch to those before being deprecated.

/cc @bobcatfish @imjasonh

Provide any links for context:

See #14216 (comment)

[stevekuznetsov]

Alternatively, can we copy paste the client types from these third-party dependencies into third_party/ to ensure that prow does not import the whole world and ameliorate all of our current issues re: imports?

/cc @cjwagner @cblecker @fejta

[fejta-bot]

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Mark the issue as fresh with /remove-lifecycle stale.
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/lifecycle stale

[vdemeester]

#15022 is merged, this can be closed
/close

[k8s-ci-robot]

@vdemeester: Closing this issue.

In response to this:

#15022 is merged, this can be closed
/close

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