[Feature flag] Cleanup use_gitaly_pagination_for_refs

Summary

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

• Previous FF issue: #372049 (closed)
• Merge request: !97137 (merged)

Owners

• Team: groupsource code
• Most appropriate slack channel to reach out to: #g_create_source-code-be
• Best individual to reach out to: @vyaklushin

What are we expecting to happen?

We expect to see less 500 errors here.

https://log.gprd.gitlab.net/goto/4a3ddb40-2778-11ed-8656-f5f2137823ba

What might happen if this goes wrong?

We still see 500 errors.

What can we monitor to detect problems with this?

https://log.gprd.gitlab.net/goto/4a3ddb40-2778-11ed-8656-f5f2137823ba

Cleaning up the feature flag

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