* Remove the `linkerd-controller` pod

Now that we got rid of the `Version` API (linkerd#6000) and the destination API forwarding business in `linkerd-controller` (linkerd#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`.

Signed-off-by: Jijeesh <jijeesh.ka@gmail.com>

Now that we no longer have a `controller` pod after #6039, there is no
need to port-forward the controller pod in the bin/web script. This
change removes the code that does that.

Signed-off-by: Dennis Adjei-Baah <dennis@buoyant.io>

Now that we no longer have a `controller` pod after #6039, there is no
need to port-forward the controller pod in the bin/web script. This
change removes the code that does that.

Signed-off-by: Dennis Adjei-Baah <dennis@buoyant.io>

Now that we no longer have a `controller` pod after linkerd#6039, there is no
need to port-forward the controller pod in the bin/web script. This
change removes the code that does that.

Signed-off-by: Dennis Adjei-Baah <dennis@buoyant.io>

Now that we no longer have a `controller` pod after linkerd#6039, there is no
need to port-forward the controller pod in the bin/web script. This
change removes the code that does that.

Signed-off-by: Dennis Adjei-Baah <dennis@buoyant.io>
Signed-off-by: Sanni Michael <sannimichaelse@gmail.com>