Deprecate unique_visits_helper in favour of redis_tracking.rb

Summary

https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/controllers/concerns/redis_tracking.rb and https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/helpers/analytics/unique_visits_helper.rb both have the same purpose, but former is more flexible. redis_tracking is also recommended by our guidelines So we can unify code by replacing unique_visits_helper usages and removing module itself.