Pulsecode,
if you need an automate solution try my plugin scan on every acf post save for unused acf or you can complete delete all before save and “resave” the field.
Still need some work but as far as i test works, you can also open a issue on github to improve it.
Works at the moment only on post and custom post type not on the taxonomy but when i have time i will improve the feature.
https://github.com/filippozanardo/redvolver-cleanacf
