Remove dependency on Kubeadm when enabling MachinePools

[salasberryfin]

/kind bug

What steps did you take and what happened:
When installing CAPZ with the MachinePools experimental feature enabled, the controller is configured to watch Kubeadm config objects, which effectively prevents users from using any other bootstrap provider other than Kubeadm.

cluster-api-provider-azure/exp/controllers/azuremachinepool_controller.go

Lines 131 to 135 in c41c0b9

	Watches(
	&kubeadmv1.KubeadmConfig{},
	handler.EnqueueRequestsFromMapFunc(KubeadmConfigToInfrastructureMapFunc(ctx, ampr.Client, log)),
	builder.WithPredicates(predicate.ResourceVersionChangedPredicate{}),
	).

What did you expect to happen:
As a user I would like to be able to use CAPZ + MachinePools with the bootstrap provider of my choice. Other providers that implement support for MachinePools do not include dependencies on Kubeadm (see CAPA).

Anything else you would like to add:
I'd like to submit a PR that removes this watcher if this is considered an accepted proposal.

Environment:

• cluster-api-provider-azure version: v1.15.0
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):