Refactoring: Reduce usages of sti_name to minimum

sti_names methods don't seem to be used.
within Edition::Identifiable:
- When edition is saved, the edition type should be propogated to the document type. Currently it is using sti_name, but Edition also has a type method. We could be using this instead.
- The published as class method is used to fetch document by slug based on the type of the subclass. So unfortunately we still need to use sti_name for this. The test however has 1 duplicate unecessary test, as we not only support News and Speeches sharing same slug, but all other document types too, which already has another test above covering that.

app/models/announcement.rb

@@ -8,10 +8,6 @@ class Announcement < Edition
   include Edition::WorldLocations
   include Edition::TopicalEvents
 
-  def self.sti_names
-    ([self] + descendants).map(&:sti_name)
-  end
-
   def self.published_with_eager_loading(ids)
     published.with_translations.includes([:document, { organisations: :translations }]).where(id: ids)
   end

app/models/concerns/edition/identifiable.rb

@@ -42,22 +42,16 @@ def update_document_slug
   end
 
   def propagate_type_to_document
-    document.document_type = self.class.document_type if document
+    document.document_type = type if document
   end
 
-  module ClassMethods
-    def document_type
-      sti_name
-    end
-
-    def published_as(slug, locale = I18n.default_locale)
-      document = Document.at_slug(document_type, slug)
-      if document.present?
-        live_edition = document.live_edition
-        return live_edition if live_edition.present? && live_edition.available_in_locale?(locale)
-      end
-      nil
+  def self.published_as(slug, locale = I18n.default_locale)
+    document = Document.at_slug(sti_name, slug)
+    if document.present?
+      live_edition = document.live_edition
+      return live_edition if live_edition.present? && live_edition.available_in_locale?(locale)
     end
+    nil
   end
 
 private

app/models/concerns/edition/publishing.rb

@@ -19,7 +19,7 @@ def by_major_change_published_at
 
     def unpublished_as(slug)
       document = Document.at_slug(document_type, slug)
-      document && document.latest_edition && document.latest_edition.unpublishing
+      document&.latest_edition&.unpublishing
     end
   end
 

app/models/edition.rb

@@ -101,7 +101,7 @@ def self.concrete_descendant_search_format_types
 
   def self.scheduled_for_publication_as(slug)
     document = Document.at_slug(document_type, slug)
-    document && document.scheduled_edition
+    document&.scheduled_edition
   end
 
   def skip_main_validation?

app/models/publicationesque.rb

@@ -16,10 +16,6 @@ class Publicationesque < Edition
 
   include ::Attachable
 
-  def self.sti_names
-    ([self] + descendants).map(&:sti_name)
-  end
-
   def self.published_with_eager_loading(ids)
     published.with_translations.includes([:document, { organisations: :translations }]).where(id: ids)
   end

test/unit/app/models/edition/identifiable_test.rb

@@ -43,14 +43,6 @@ class Edition::IdentifiableTest < ActiveSupport::TestCase
     assert_equal publication.document.slug, news_article.document.slug
   end
 
-  test "should allow the same slug to be used for a news article and a speech" do
-    same_title = "same-title"
-    news_article = create(:news_article, title: same_title)
-    speech = create(:speech, title: same_title)
-
-    assert_equal news_article.document.slug, speech.document.slug
-  end
-
   test "should return the edition of the correct type when matching slugs for other types exist" do
     same_title = "same-title"
     news_article = create(:published_news_article, title: same_title)