[Feature flag] Cleanup ff_pages_use_open_file

Summary

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

We are removing feature flag ff_pages_use_open_file to keep the new approach.

Owners

• Team: Plan::Knowledge
• Most appropriate slack channel to reach out to: #g_knowledge
• Best individual to reach out to: @ngala
• PM: @mmacfarlane

Stakeholders

Expectations

What might happen if this goes wrong?

Pages deploy jobs fail.

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 ff_pages_use_open_file 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 ff_pages_use_open_file --dev --pre --staging --staging-ref --production
• Close this rollout issue.