artists: reduce queries in artist summaries.

Avoid a few queries when searching for single artist tags.

test/unit/artist_test.rb

@@ -64,21 +64,6 @@ class ArtistTest < ActiveSupport::TestCase
       should_not allow_value("").for(:name)
     end
 
-    context "with a matching tag alias" do
-      setup do
-        @tag_alias = FactoryBot.create(:tag_alias, :antecedent_name => "aaa", :consequent_name => "bbb")
-        @artist = FactoryBot.create(:artist, :name => "aaa")
-      end
-
-      should "know it has an alias" do
-        assert_equal(true, @artist.has_tag_alias?)
-      end
-
-      should "know its alias" do
-        assert_equal("bbb", @artist.tag_alias_name)
-      end
-    end
-
     context "that has been banned" do
       setup do
         @post = FactoryBot.create(:post, :tag_string => "aaa")