docs: Simplify preflight migrate-identity example
docs: Simplify preflight migrate-identity example

The command is able to derive the configuration from the environment the
same way cilium-agent does. The example now reflects this.

Signed-off-by: Ray Bejjani <7f525154e857f3d57a641a83dddc584f42addc6a@isovalent.com>

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