Revert "Generate a schema for the ProwJob crd (#19522)"

[chaodaiG]

This reverts commit 914737a.

Seems like server side apply didn't work:
https://prow.k8s.io/view/gs/kubernetes-jenkins/logs/post-test-infra-deploy-prow/1436369391678656512

[chaodaiG]

/cc @alvaroaleman

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[chaodaiG]

This was an attempt to pass --server-side=true to kubectl apply for the generated prowjob CRD, since it's too large to be applied on client side. I thought this would work as mentioned in #19522 (comment), but somehow it didn't work. The postsubmit job https://prow.k8s.io/view/gs/kubernetes-jenkins/logs/post-test-infra-deploy-prow/1436369391678656512 failed with:

$ /usr/bin/kubectl --kubeconfig= --cluster=gke_k8s-prow_us-central1-f_prow --context= --user= apply -f -
The CustomResourceDefinition "prowjobs.prow.k8s.io" is invalid: 
* metadata.annotations: Too long: must have at most 262144 bytes
* spec.preserveUnknownFields: Invalid value: true: must be false in order to use defaults in the schema

Note that --server-side=true was not included in the command.

• @fejta here in case you know how to achieve this