Don't require `API::API` in routes

`API::API` is autoloaded and shouldn't be required in non-autoloaded
code. Otherwise, we get the following dreaded error:

  A copy of API::Helpers has been removed from the module tree but is
  still active!

Signed-off-by: Rémy Coutable <remy@rymai.me>

config/routes.rb

 require 'sidekiq/web'
 require 'sidekiq/cron/web'
-require 'api/api'
 require 'constraints/group_url_constrainer'
 Rails.application.routes.draw do