Revert "Add agency to dois response (#1276)"

This reverts commit 1deddbb.

app/serializers/datacite_doi_serializer.rb

@@ -18,7 +18,6 @@ class DataciteDoiSerializer
              :titles,
              :publisher,
              :container,
-             :agency,
              :publication_year,
              :subjects,
              :contributors,

spec/requests/datacite_dois/datacite_dois_spec.rb

@@ -438,17 +438,6 @@ def clear_doi_index
     end
   end
 
-  describe "GET /dois/:id with agency values", prefix_pool_size: 1 do
-    let!(:doi) { create(:doi, client: client, aasm_state: "findable") }
-
-    it "returns agency values" do
-      get "/dois/#{doi.doi}", nil, headers
-
-      expect(last_response.status).to eq(200)
-      expect(json.dig("data", "attributes", "agency")).to eq("datacite")
-    end
-  end
-
   describe "GET /dois with client-type filter", prefix_pool_size: 3 do
     let!(:dois) { create_list(:doi, 10, client: client, aasm_state: "findable", version_info: "testtag") }
     let(:client_igsn_id_catalog) { create(:client, provider: provider, client_type: "igsnCatalog") }