models: remove belongs_to_creator macro.

The belongs_to_creator macro was used to initialize the creator_id field
to the CurrentUser. This made tests complicated because it meant you had
to create and set the current user every time you wanted to create an
object, when lead to the current user being set over and over again. It
also meant you had to constantly be aware of what the CurrentUser was in
many different contexts, which was often confusing. Setting creators
explicitly simplifies everything greatly.

test/unit/artist_test.rb

@@ -30,27 +30,27 @@ class ArtistTest < ActiveSupport::TestCase
     end
 
     should "parse inactive urls" do
-      @artist = Artist.create(name: "blah", url_string: "-http://monet.com")
+      @artist = create(:artist, name: "blah", url_string: "-http://monet.com")
       assert_equal(["-http://monet.com"], @artist.urls.map(&:to_s))
       refute(@artist.urls[0].is_active?)
     end
 
     should "not allow duplicate active+inactive urls" do
-      @artist = Artist.create(name: "blah", url_string: "-http://monet.com\nhttp://monet.com")
+      @artist = create(:artist, name: "blah", url_string: "-http://monet.com\nhttp://monet.com")
       assert_equal(1, @artist.urls.count)
       assert_equal(["-http://monet.com"], @artist.urls.map(&:to_s))
       refute(@artist.urls[0].is_active?)
     end
 
     should "allow deactivating a url" do
-      @artist = Artist.create(name: "blah", url_string: "http://monet.com")
+      @artist = create(:artist, name: "blah", url_string: "http://monet.com")
       @artist.update(url_string: "-http://monet.com")
       assert_equal(1, @artist.urls.count)
       refute(@artist.urls[0].is_active?)
     end
 
     should "allow activating a url" do
-      @artist = Artist.create(name: "blah", url_string: "-http://monet.com")
+      @artist = create(:artist, name: "blah", url_string: "-http://monet.com")
       @artist.update(url_string: "http://monet.com")
       assert_equal(1, @artist.urls.count)
       assert(@artist.urls[0].is_active?)
@@ -69,7 +69,7 @@ class ArtistTest < ActiveSupport::TestCase
         @post = FactoryBot.create(:post, :tag_string => "aaa")
         @artist = FactoryBot.create(:artist, :name => "aaa")
         @admin = FactoryBot.create(:admin_user)
-        CurrentUser.scoped(@admin) { @artist.ban! }
+        @artist.ban!(banner: @admin)
         @post.reload
       end
 
@@ -542,7 +542,7 @@ class ArtistTest < ActiveSupport::TestCase
     context "#new_with_defaults" do
       should "fetch the defaults from the given source" do
         source = "https://i.pximg.net/img-original/img/2018/01/28/23/56/50/67014762_p0.jpg"
-        artist = Artist.new_with_defaults(source: source)
+        artist = Artist.new_with_defaults(source: source, creator: create(:user))
 
         assert_equal("niceandcool", artist.name)
         assert_equal("nice_and_cool", artist.other_names_string)