Remove kube-apiserver PrometheusRule from manifests

0000_90_kube-apiserver-operator_04_servicemonitor-apiserver lists Prometheus Rule `kube-apiserver` which is meant to be deleted by CVO (has `release.openshift.io/delete: "true"` annotation).
This manifests is no longer needed, as `cluster:apiserver_current_inflight_requests:sum:max_over_time:2m` recording rule is already provided by other PrometheusRules.

If this is meant to be removed in 4.13, its safe to remove the manifest in 4.14, as we don't allow skipping 4.13 and by the time users will start 4.14 update this manifest would already be removed in the clusters by CVO

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