models: include all int/bool columns as html data attributes by default.

app/models/dmail.rb

@@ -146,16 +146,9 @@ class Dmail < ApplicationRecord
     end
   end
 
-  module ApiMethods
-    def html_data_attributes
-      [:owner_id, :from_id, :to_id, :is_read?]
-    end
-  end
-
   include AddressMethods
   include FactoryMethods
   extend SearchMethods
-  include ApiMethods
 
   def validate_sender_is_not_banned
     if from.try(:is_banned?)