[Feature flag cleanup] Remove top_level_group_creation_enabled

Summary

This issue is to cleanup the top_level_group_creation_enabled feature flag after the feature flag has been enabled by default for an appropriate amount of time in production.

• The feature flag has been removed in the codebase
• This issue will handle its deletion on all environments via chatops

Owners

• Team: groupauthentication
• Most appropriate slack channel to reach out to: #g_scss_authentication
• Best individual to reach out to: @habdul-razak
• PM: @hsutor

Stakeholders

EM - @adil.farrukh

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 top_level_group_creation_enabled 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 https://gitlab.com/gitlab-org/gitlab/-/merge_requests/187738
• 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 top_level_group_creation_enabled --dev --pre --staging --staging-ref --production
• Close this rollout issue.