Merge branch 'add-feature-flag-cleanup-to-template' into 'master'

Document cleanup of feature flag after deploy

See merge request gitlab-org/gitlab-ce!31893

.gitlab/issue_templates/Feature Flag Roll Out.md

@@ -39,5 +39,6 @@ If applicable, any groups/projects that are happy to have this feature turned on
 - [ ] Cross post chatops slack command to `#support_gitlab-com` and in your team channel
 - [ ] Announce on the issue that the flag has been enabled
 - [ ] Remove feature flag and add changelog entry
+- [ ] After the flag removal is deployed, [clean up the feature flag](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up) by running chatops command in `#production` channel
 
 /label ~"feature flag"