Refactor services to match EE signature

Refactor Users::UpdateService and EmailsXX::Service to match EE signature, as part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2103

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?