Readd admin tab to retired documents

This was originally removed as you can change document format from this
tab but the tab also houses the delete draft feature which we need.

app/helpers/tabs_helper.rb

@@ -25,9 +25,8 @@ def tabs
   def tabs_for(user, resource)
     tabs_to_remove = []
     tabs_to_remove << "admin" unless user.has_editor_permissions?(resource)
-    tabs_to_remove << "admin" if resource.retired_format?
     tabs_to_remove << "unpublish" unless user.govuk_editor?
 
-    tabs.reject { |tab| tabs_to_remove.uniq.include?(tab.name) }
+    tabs.reject { |tab| tabs_to_remove.include?(tab.name) }
   end
 end

test/unit/tabs_helper_test.rb

@@ -58,11 +58,5 @@ class TabsHelperTest < ActionView::TestCase
       user = FactoryBot.create(:user, :welsh_editor)
       assert_equal %w[admin unpublish], (tabs - tabs_for(user, guide)).map(&:name)
     end
-
-    should "exclude `admin` tab if document retired" do
-      retired_document = FactoryBot.create(:campaign_edition)
-      user = FactoryBot.create(:user, :govuk_editor)
-      assert_equal %w[admin], (tabs - tabs_for(user, retired_document)).map(&:name)
-    end
   end
 end