[CE] Fix rails 5 deprecation warnings

What does this MR do?

CE backport of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7324

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides