database: remove duplicate users_with_backend migration

				alter table backends add column motis bool default false;

				alter table schema_version add column motis varchar(12);

				drop view users_with_backend;

				create view users_with_backend as select

					users.id as id, users.name as name, status, public_level,

					email, password, registered_at, last_seen,

					deletion_requested, deletion_notified, use_history,

					accept_follows, notifications, profile, backend_id, iris,

					hafas, efa, dbris, motis, backend.name as backend_name

					from users

					left join backends as backend on users.backend_id = backend.id

					;

				create table stations_external_ids (

					eva serial not null primary key,

					backend_id smallint not null,