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kubeadm: Deduplicate kube-proxy image logic

**What this PR does / why we need it**:

Until now, kube-proxy image was handled in two separate places:
    
- In images.go along with the pre-pull code and without having the image override capabilities (via UnifiedControlPlaneImage)

- In the kube-proxy manifest, where image override was possible.

This duplicates the kube-proxy image logic and makes it prone to errors.
Therefore, this change aims to deduplicate it and make it more straightforward.
This is achieved in the following ways:

- GetKubeControlPlaneImage is used for kube-proxy image fetching, thus allowing for the image to be overriden by UnifiedControlPlaneImage.

- Remove duplicated logic from the manifest and use GetKubeControlPlaneImage to generate the image for the manifest.

This PR also removes GetKubeControlPlaneImageNoOverride as it's no longer needed.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
None

**Special notes for your reviewer**:

/cc @kubernetes/sig-cluster-lifecycle-pr-reviews
/area kubeadm
/assign @luxas
/assign @timothysc

**Release note**:

```release-note
kubeadm: make sure pre-pulled kube-proxy image and the one specified in its daemon set manifest are the same
```