Remove all references to cluster-api-bootstrap-provider-kubeadm

This repository has been inactive for a long time, and it's due for
archival.

Signed-off-by: Vince Prignano <[email protected]>

Author: vincepri

sig-cluster-lifecycle/README.md

@@ -63,7 +63,6 @@ The following [subprojects][subproject-definition] are owned by sig-cluster-life
     - [Meeting notes and Agenda](https://docs.google.com/document/d/10_tl_SXcFGb-2109QpcFVrdrfnVEuQ05MBrXtasB0vk/edit).
 ### cluster-api
 - **Owners:**
-  - [kubernetes-sigs/cluster-api-bootstrap-provider-kubeadm](https://github.com/kubernetes-sigs/cluster-api-bootstrap-provider-kubeadm/blob/master/OWNERS)
   - [kubernetes-sigs/cluster-api](https://github.com/kubernetes-sigs/cluster-api/blob/master/OWNERS)
 - **Contact:**
   - Slack: [#cluster-api](https://kubernetes.slack.com/messages/cluster-api)

sigs.yaml

@@ -984,7 +984,6 @@ sigs:
     contact:
       slack: cluster-api
     owners:
-    - https://raw.githubusercontent.com/kubernetes-sigs/cluster-api-bootstrap-provider-kubeadm/master/OWNERS
     - https://raw.githubusercontent.com/kubernetes-sigs/cluster-api/master/OWNERS
     meetings:
     - description: Cluster API office hours