Fix for 'OK' messages being sent to users going through SMS game flow

#### What's this PR do?
This removes the 200 status code that the app responds with when successfully progressing through an SMS game.

With the 200 code, users would get the 'OK' message on their phones in addition to the opt-in message that we're subscribing them to. Not specifying a status code seems fine, and still serves the purpose of acknowledging receipt of the request.

#### What are the relevant tickets?
https://github.com/jonuy/ds-mdata-responder/issues/2