Responses schema fixes (#3650)

Fixes #2237.

Corrects the response schemas for:

```
PUT /user/{user_id}/account_data/{account_dataType}
PUT /user/{user_id}/rooms/{roomId}/account_data/{type}
PUT /directory/list/room/{roomId}
PUT /sendToDevice/{eventType}/{txnId}
POST /account/3pid
POST /account/3pid/add
POST /account/3pid/bind
```

data/api/client-server/list_public_rooms.yaml

@@ -104,6 +104,8 @@ paths:
           description: The visibility was updated, or no change was needed.
           examples:
             application/json: {}
+          schema:
+            type: object
         404:
           description: The room is not known to the server
           examples: