plugins/cilium-cni: uninstall cilium-flannel CNI configuration if user opt-in
plugins/cilium-cni: uninstall cilium-flannel CNI configuration if user opt-in

This avoids containers to accidentally be created and starting being
managed only by Flannel if Cilium is in the process of being upgraded
where the CNI configuration is always removed during the upgrade.

Signed-off-by: André Martins <bc9800b9d52a24cce72a73dd528afed53f10e5fc@cilium.io>

michi-covalent/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,cilium-team/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,cilium-team/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium