Remove deprecated attributes from SiteCustomization::Page

Some fields from SiteCustomization::page are translatable and we no
longer need them. This commit will remove the annoying deprecation
warning thrown by Globalize gem after gem version update.

db/migrate/20190221171859_remove_deprecated_translatable_fields_from_site_customization_pages.rb

@@ -0,0 +1,7 @@
+class RemoveDeprecatedTranslatableFieldsFromSiteCustomizationPages < ActiveRecord::Migration[4.2]
+  def change
+    remove_column :site_customization_pages, :title, :string
+    remove_column :site_customization_pages, :subtitle, :string
+    remove_column :site_customization_pages, :content, :text
+  end
+end