My question is similar, in that I build sites on a subdomain and once site is ready, I use the migrator feature to transfer to permanent domain. I then deactivate and delete the backup plugin and either delete the testing site altogether, or park it in case further tests are needed. This is my normal workflow.
Obviously I have no need to maintaining a copy of Updraft Premium on the development site, and you will become pretty annoyed at me always asking for the licenses to be reset.
What’s the best way to do this? the licenses that remain active are for clients who have me monitor their backups on an annual basis, so I don’t see any of those going away. As soon as I hit my limit of permanent sites, I will be upgrading to a larger plan.