Remove unused Go operator scaffold code

[hasbro17]

Description of the change:
Remove unused scaffolding code for Go operators.

Motivation for the change:
Follow up from #3190 (review)

[hasbro17]

Ah whoops, removed too much.
Going to add back the bits that we actually still need.

[camilamacedo86]

yes, we still need the scaffold used in the add command. otherwise, it shows good.

[hasbro17]

Turns out pretty much everything in internal/scaffold is still being used by one cmd or the other in the legacy CLI.
So not a whole lot here until that gets removed.

[estroz]

/lgtm

Thoughts on making a kubebuilder PR for internal/scaffold/version.go? Its a nice-to-have for operators.

[hasbro17]

@estroz I'm not opposed but I imagine scaffolding a version/version.go for operator projects is one of those things that Kubebuilder probably won't want to be opinionated about since it doesn't have much to do with the workflow of writing controllers/operators.

Plus other projects in the wild each have their own preference of where to place the version information.
https://github.com/jetstack/cert-manager/blob/master/cmd/ctl/pkg/version/version.go
https://github.com/coreos/prometheus-operator/blob/master/VERSION
https://github.com/oracle/mysql-operator/blob/master/pkg/version/version.go
https://github.com/zalando/postgres-operator/blob/master/kubectl-pg/cmd/version.go
https://github.com/rook/rook/blob/master/pkg/version/version.go#L19
https://github.com/vmware-tanzu/velero/blob/master/pkg/buildinfo/version.go#L26

So I imagine that might be out of scope for Kubebuilder.