fix: remove label already set in input data

[eatondustin1]

This fixes the following error when applying manifests:

apply-manifests error: ApplySet label "applyset.kubernetes.io/part-of" already set in input data

Before

```json { "apiVersion": "kubecfg.dev/v1alpha1", "kind": "AppInstance", "metadata": { "creationTimestamp": "2024-04-22T15:32:01Z", "finalizers": [ "kubecfg.dev/appinstance-cleanup" ], "generation": 2, "labels": { "applyset.kubernetes.io/part-of": "applyset-mBM9N2j2qchpaBrvdpdvR14sxslSY3xXQErluXJpNgE-v1", "kustomize.toolkit.fluxcd.io/name": "flux-system", "kustomize.toolkit.fluxcd.io/namespace": "flux-system" }, "name": "podinfo", "namespace": "default", "resourceVersion": "16394167", "uid": "52d8b18a-dc24-4d73-9086-a3a308b5da6a" }, "spec": { "package": { "image": "***/podinfo:v0.0.3", "apiVersion": "demo/v1alpha1", "spec": { "bar": "baz", "foo": "bar" } }, "imagePullSecrets": [ { "name": "artifact-registry" } ], "pause": true } } ```

After

```json { "apiVersion": "kubecfg.dev/v1alpha1", "kind": "AppInstance", "metadata": { "creationTimestamp": "2024-04-22T15:32:01Z", "finalizers": [ "kubecfg.dev/appinstance-cleanup" ], "generation": 2, "labels": { "kustomize.toolkit.fluxcd.io/name": "flux-system", "kustomize.toolkit.fluxcd.io/namespace": "flux-system" }, "name": "podinfo", "namespace": "default", "resourceVersion": "16394167", "uid": "52d8b18a-dc24-4d73-9086-a3a308b5da6a" }, "spec": { "package": { "image": "***/podinfo:v0.0.3", "apiVersion": "demo/v1alpha1", "spec": { "bar": "baz", "foo": "bar" } }, "imagePullSecrets": [ { "name": "artifact-registry" } ], "pause": true } } ```