docs: cleanup and tidy up the 1.11 upgrade guide
docs: cleanup and tidy up the 1.11 upgrade guide

This upgrade guide contained all other versions in it. To prevent users
from mistakenly reading an old upgrade guide, we should remove those
leftovers.

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

michi-covalent/cilium,cilium/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium