Remove cert manager dependency for Opni agent

[dbason]

Error: unable to build kubernetes objects from release manifest: [resource mapping not found for name: "opni-agent-webhook-cert" namespace: "opni-system" from "": no matches for kind "Certificate" in version "cert-manager.io/v1"
ensure CRDs are installed first, resource mapping not found for name: "opni-agent-selfsigned-issuer" namespace: "" from "": no matches for kind "Issuer" in version "cert-manager.io/v1"
ensure CRDs are installed first]

Should remove this from the helmchart and confirm it's no longer required. Agent should not require cert manager