Remove Group#owner_id from API since it is not used any more

CHANGELOG

@@ -57,6 +57,7 @@ v 7.8.0 (unreleased)
   - Add quick help links to the GitLab pricing and feature comparison pages.
   - Fix duplicate authorized applications in user profile and incorrect application client count in admin area.
   - Make sure Markdown previews always use the same styling as the eventual destination.
+  - Remove deprecated Group#owner_id from API
 
 v 7.7.2
   - Update GitLab Shell to version 2.4.2 that fixes a bug when developers can push to protected branch

doc/api/groups.md

@@ -14,7 +14,6 @@ GET /groups
     "id": 1,
     "name": "Foobar Group",
     "path": "foo-bar",
-    "owner_id": 18,
     "description": "An interesting group"
   }
 ]
@@ -87,7 +86,6 @@ GET /groups?search=foobar
     "id": 1,
     "name": "Foobar Group",
     "path": "foo-bar",
-    "owner_id": 18,
     "description": "An interesting group"
   }
 ]

lib/api/entities.rb

@@ -65,7 +65,7 @@ module API
     end
 
     class Group < Grape::Entity
-      expose :id, :name, :path, :owner_id, :description
+      expose :id, :name, :path, :description
     end
 
     class GroupDetail < Group

lib/api/groups.rb

@@ -33,9 +33,9 @@ module API
 
         attrs = attributes_for_keys [:name, :path, :description]
         @group = Group.new(attrs)
-        @group.owner = current_user
 
         if @group.save
+          @group.add_owner(current_user)
           present @group, with: Entities::Group
         else
           render_api_error!("Failed to save group #{@group.errors.messages}", 400)