Try to make benchmarks fair

Currently, the benchmarks are not fair because some apps return a 200 for
all requests, and other apps return 200 only for GET /. The apps that return
200 only for GET / obviously have to do more work, so they shouldn't get
penalized for it.

This fixes the following issues:

* The cuba, rack, and rack-response apps all return 200 for all requests, not
  just GET /.
* The mustermann app returns 200 for any request method with /, not just GET /.
* The lotus-router app doesn't return a rack response that is valid according
  to Rack::Lint.

This also removes unused routes from the lotus-router and mustermann apps.