[Feature flag] Cleanup admin_projects_vue

Summary

This issue is to cleanup the admin_projects_vue feature flag. We left the feature flag in for one milestone to de-risk release since it is an admin area feature that does not get the same amount of traffic as a typical gitlab.com feature. Assuming there are no issues, this feature flag should be removed in %18.4 along with the legacy HAML templates.

Owners

• Team: grouporganizations
• Most appropriate slack channel to reach out to: #g_organizations
• Best individual to reach out to: @smaglangit
• PM: @lohrc

Expectations

Cleaning up the feature flag

• Specify in the issue description if this feature will be removed completely or will be productized as part of the Feature Flag cleanup
• Create a merge request to remove <feature-flag-name> feature flag. Ask for review and merge it.
  • Remove all references to the feature flag from the codebase.
  • Remove the YAML definitions for the feature from the repository.
  • Create a changelog entry.
• Ensure that the cleanup MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post.
  • /chatops run auto_deploy status <merge-commit-of-cleanup-mr>
• Close the feature issue to indicate the feature will be released in the current milestone.
• If not already done, clean up the feature flag from all environments by running these chatops command in #production channel: /chatops run feature delete <feature-flag-name> --dev --pre --staging --staging-ref --production
• Close this rollout issue.