Remove scaffolding specific to operator-sdk

[mitchnielsen]

Summary

Removes the operator-sdk-specific scaffolding, instead relying only on the scaffolding from kubebuilder.

We don't currently have plans to push to ArtifactHub or OLM, so let's remove it for now.

References

• https://book.kubebuilder.io/cronjob-tutorial/basic-project.html
• https://github.com/kubernetes-sigs/kubebuilder/tree/master/docs/book/src/cronjob-tutorial/testdata/project
• https://sdk.operatorframework.io/docs/overview/project-layout