Rails5 deprecation: :nothing option is deprecated, Use head method to respond with empty response body.

What does this MR do?

Fixes DEPRECATION WARNING: ':nothing' option is deprecated and will be removed in Rails 5.1. Use 'head' method to respond with empty response body.

Deprecations in EE: gitlab-ee!8560

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
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.