Fix project export presenter

- Fix specs for #description method
- Remove as_json override, use description method

app/presenters/projects/import_export/project_export_presenter.rb

@@ -3,14 +3,16 @@
 module Projects
   module ImportExport
     class ProjectExportPresenter < Gitlab::View::Presenter::Delegated
+      include ActiveModel::Serializers::JSON
+
       presents :project
 
       def project_members
         super + converted_group_members
       end
 
-      def as_json(*_args)
-        self.respond_to?(:override_description) ? super.merge("description" => override_description) : super
+      def description
+        self.respond_to?(:override_description) ? override_description : super
       end
 
       private

spec/presenters/projects/import_export/project_export_presenter_spec.rb

@@ -5,26 +5,44 @@ require 'spec_helper'
 describe Projects::ImportExport::ProjectExportPresenter do
   let_it_be(:group) { create(:group) }
   let_it_be(:project) { create(:project, group: group) }
-  let_it_be(:project) { create(:project, group: group) }
   let_it_be(:user) { create(:user) }
+
+  subject { described_class.new(project, current_user: user) }
+
+  describe '#description' do
+    context "override_description not provided" do
+      it "keeps original description" do
+        expect(subject.description).to eq(project.description)
+      end
+    end
+
+    context "override_description provided" do
       let(:description) { "overridden description" }
 
       subject { described_class.new(project, current_user: user, override_description: description) }
 
-  describe '#as_json' do
-    context "override_description provided" do
       it "overrides description" do
-        expect(subject.as_json["description"]).to eq(description)
+        expect(subject.description).to eq(description)
+      end
     end
   end
 
+  describe '#as_json' do
     context "override_description not provided" do
-      subject { described_class.new(project, current_user: user) }
-
       it "keeps original description" do
         expect(subject.as_json["description"]).to eq(project.description)
       end
     end
+
+    context "override_description provided" do
+      let(:description) { "overridden description" }
+
+      subject { described_class.new(project, current_user: user, override_description: description) }
+
+      it "overrides description" do
+        expect(subject.as_json["description"]).to eq(description)
+      end
+    end
   end
 
   describe '#project_members' do