Fix remaining Registration V2 issues

[FinnIckler]

About halfway done going through https://docs.google.com/spreadsheets/d/1VQXDGVdYgmoH5hWpUI6wzla6NhZ4rMGbuDcHOc9ODH8/edit#gid=1116831171

Am I correct using

pending_registrations = if @competition.uses_new_registration_service?
                                      Microservices::Registrations.registrations_by_competition(@competition.id, 'pending', cache: false)
                                      else
                                        @competition.registrations.pending.count
                                      end

here? I am still not 100% sure when to use microservice_registrations instead of calling directly.