CF-346: remove /metadata and /

Per discussion with @ChandraAddala and @usnavi, we decided that it would be best to remove the following requests:
```
GET /metadata
GET /
```
I couldn't really remove the ```GET /```, because removing the Scalatra route makes the request be routed to Jetty, which displays the directory structure under the webapp. I don't think we want that. So I decided to code the get("/") to return 404.
@ChandraAddala, actually, I think we still need the regex, because we still have request URIs ```/metadata/:preference_type```