Lightroom 5 does not use activation technology so it is not necessary.
Why must ADOBE make things so complicated?
I don't think there's much out there that's less complicated than "don't do anything..."
It used to be so easy, go to HELP, then "Deactivate".
Not in Lightroom. Not ever, historically.
I had the same question once and asked the support hotline for help. Just uninstall Lightroom. Deactivating is not necessary.