[Feature Flag] Cleanup :new_vulnerability_form flag and related code

Summary

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

Owners

• Team: Threat Insights
• Most appropriate slack channel to reach out to: #g_threat_insights
• Best individual to reach out to: @svedova
• PM: @matt_wilson

What might happen if this goes wrong?

Manual creation of the vulnerabilities can be affected.

Cleaning up the feature flag

• Create a merge request to remove new_vulnerability_form 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 new_vulnerability_form --dev
  • /chatops run feature delete new_vulnerability_form --staging
  • /chatops run feature delete new_vulnerability_form
• Close this rollout issue.