[Feature flag] Cleanup vue_issues_list

Summary

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

• Remove FF in QA specs
• Remove FF in feature specs
• Remove FF in backend code and specs
• Remove FF in frontend code and specs (including unused CSS and Ruby methods/instance variables referenced in Haml)

Related issues:

• Feature issue: #322755 (closed)
• Feature flag rollout issue: #323743 (closed)

Owners

• Team: groupproject management
• Most appropriate slack channel to reach out to: #s_plan
• Best individual to reach out to: @cngo
• PM: @gweaver

Stakeholders

Expectations

What might happen if this goes wrong?

Cleaning up the feature flag

• Create a merge request to remove vue_issues_list 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.
• Clean up the feature flag from all environments by running these chatops command in #production channel:
  • /chatops run feature delete vue_issues_list --dev
  • /chatops run feature delete vue_issues_list --staging
  • /chatops run feature delete vue_issues_list
• Close this rollout issue.