[Feature flag] Cleanup inherit_higher_access_levels_no_cross_join

Summary

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

Owners

• Team: ~"group::authentication and authorization"
• Most appropriate slack channel to reach out to: #g_govern_auth
• Best individual to reach out to: @dblessing, @tkuah
• PM: @hsutor

Stakeholders

• @lohrc grouptenant scale PM

Expectations

What might happen if this goes wrong?

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 inherit_higher_access_levels_no_cross_join feature flag. Ask for review and merge it.

Please also remove the allow_cross_joins_across_databases in ee/lib/ee/gitlab/auth/ldap/sync/group.rb

- [ ] Remove all references to the feature flag from the codebase.
- [ ] Remove the YAML definitions for the feature from the repository.
- [ ] Create [a changelog entry](https://docs.gitlab.com/ee/development/feature_flags/#changelog).

• 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 inherit_higher_access_levels_no_cross_join --dev --staging --staging-ref --production
• Close this rollout issue.