Remove legacy routes

Remove legacy routes

• Group routes introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15052
  • CE => https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29351
  • EE => https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14256
• Project routes introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28435
• User routes introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6851
  • CE https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30044
  • EE https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14382