Fix tests for format specifier in providers’ configurations

As `oauth1.coffee` uses `request_token.format` and `access_token.format` (see [oauth1.coffee](https://github.com/oauth-io/oauthd/blob/3cdabf1dbda7a7ea406625160f7fd1e2405bab01/lib/oauth1.coffee) – L102, L104, L209, L211) the tests shouldn’t throw a warning if they are used. Furthermore, the tests allowed `application/json` and `application/x-www-form-urlencoded` as a value for `access_token.format` and `refresh.format`, however, the actual `oauth2.coffee` didn’t check for these values, so I removed them.