Ah, that's not what consideration means in contract law. Consideration means something is exchanged for something else. (See https://en.wikipedia.org/wiki/Consideration_in_English_law)

You could argue that the indefinite API access was in exchange for writing the app (service for service), but if this were me, I probably wouldn't bother. Maybe I'd write an adversarial-interoperability backend to replace the API, or open-source the app to allow other interested parties to do so. Or maybe I'd just say "It was a nice run", and let it die.

If you care enough to send a polite email, you could say that Yelp has a prior agreement, you'd appreciate them not reneging, and if they do, you'd appreciate compensation for your labour (minus, of course, the money you made from the software). Probably won't go anywhere, but…