Remove unused errors on attachment methods

They aren't used since commit f8d78ec4a.

app/helpers/documents_helper.rb

@@ -3,10 +3,6 @@ module DocumentsHelper
     document.attachment_file_name
   end
 
-  def document_errors_on_attachment(document)
-    document.errors[:attachment].join(", ") if document.errors.key?(:attachment)
-  end
-
   def render_destroy_document_link(builder, document)
     if !document.persisted? && document.cached_attachment.present?
       link_to t("documents.form.delete_button"),

app/helpers/images_helper.rb

@@ -13,10 +13,6 @@ module ImagesHelper
     image.attachment_file_name
   end
 
-  def image_errors_on_attachment(image)
-    image.errors[:attachment].join(", ") if image.errors.key?(:attachment)
-  end
-
   def image_class(image)
     image.persisted? ? "persisted-image" : "cached-image"
   end