* Remove the `linkerd-controller` pod
Now that we got rid of the `Version` API (#6000) and the destination API forwarding business in `linkerd-controller` (#5993), we can get rid of the `linkerd-controller` pod.
## Removals
- Deleted everything under `/controller/api/public` and `/controller/cmd/public-api`.
- Moved `/controller/api/public/test_helper.go` to `/controller/api/destination/test_helper.go` because those are really utils for destination testing. I also extracted from there the prometheus mock structs and put that under `/pkg/prometheus/test_helper.go`, which is now by both the `linkerd diagnostics endpoints` and the `metrics-api` tests, removing some duplication.
- Deleted the `controller.yaml` and `controller-rbac.yaml` helm templates along with the `publicAPIResources` and `publicAPIProxyResources` helm values.
## Health checks
- Removed the `can initialize the client` check given such client is no longer needed. The `linkerd-api` section was left with only the check `control pods are ready`, so I moved that under the `linkerd-existence` section and got rid of the `linkerd-api` section altogether.
- In that same `linkerd-existence` section, got rid of the `controller pod is running` check.
## Other changes
- Fixed the Control Plane section of the dashboard, taking account the disappearance of `linkerd-controller` and previously, of `linkerd-sp-validator`.
dependabot[bot]
Alejandro Pedraza