Merge branch 'selhorn-ff-legacy-remove' into 'master'

Redirected old feature flag page

See merge request gitlab-org/gitlab!83468

doc/api/feature_flags_legacy.md

 ---
-stage: Release
-group: Release
-info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+redirect_to: 'feature_flags.md'
+remove_date: '2022-06-22'
 ---
 
-# Legacy Feature Flags API **(FREE)**
+This document was moved to [another location](feature_flags).
 
-> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/9566) in GitLab Premium 12.5.
-> - [Moved](https://gitlab.com/gitlab-org/gitlab/-/issues/212318) to GitLab Free in 13.5.
-
-This API was removed in [GitLab 14.0](https://gitlab.com/gitlab-org/gitlab/-/issues/213369).
-Please use [the new API](feature_flags.md) instead.
+<!-- This redirect file can be deleted after <2022-06-22>. -->
+<!-- Redirects that point to other docs in the same project expire in three months. -->
+<!-- Redirects that point to docs in a different project or site (for example, link is not relative and starts with `https:`) expire in one year. -->
+<!-- Before deletion, see: https://docs.gitlab.com/ee/development/documentation/redirects.html -->
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