[Spike] Investigate removal of CRDs

Summary

The following discussion from !508 (merged) should be addressed:

• @mnielsen started a discussion: (+8 comments)

  @dmakovey is it also safe to remove controllers/testdata/crds/crd-certificates.yaml?

---

Let's investigate if we can remove:

crd-certificaterequests.yaml
crd-certificates.yaml
crd-challenges.yaml
crd-clusterissuers.yaml
crd-issuers.yaml
crd-orders.yaml
k8s.nginx.org_nginxingresscontrollers_crd.yaml
monitoring.coreos.com_servicemonitors.yaml

Acceptance

• Above CRDs/manifests (and any others in the project) are investigated to confirm whether or not they are needed
• If any can be deleted, open a follow-up issue to remove them