docs: Updates steps when using submit-backport
docs: Updates steps when using submit-backport

The submit-backport script takes care of pushing the local branch to the
remote repository. So, when using that script, the push step is
unnecessary.

Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

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