[Feature flag] Cleanup blame_page_streaming

Summary

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

This new feature enables streaming of the full blame page and replaces a buffered variant of the page. Learn more about HTML streaming.

Owners

• Team: groupcode review
• Most appropriate slack channel to reach out to: #g_create_source-code-review-fe
• Best individual to reach out to: @slashmanov
• PM: @andr3

Stakeholders

• Manager: @andr3
• Test engineer (perf metrics): @niskhakova
• groupsource code frontend maintainer: @jerasmus

Expectations

What might happen if this goes wrong?

Revert the cleanup MR.

Cleaning up the feature flag

• 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
  • /chatops run feature delete <feature-flag-name> --staging
  • /chatops run feature delete <feature-flag-name>
• Close this rollout issue.