Due to the way that rswag expands shared components we were getting this
warning when linting our api docs:
```
Component: "user_response" is never used.
```
This change refactors the `api/users_spec.rb` file so that it uses the
new way of doing things with a separate `user_get_response.json` schema
file rather then the old way of loading a shared response inside of the
swagger_helper.rb file.
