reset_callbacks

# File activesupport/lib/active_support/callbacks.rb, line 686
      def reset_callbacks(name)
        callbacks = get_callbacks name

        ActiveSupport::DescendantsTracker.descendants(self).each do |target|
          chain = target.get_callbacks(name).dup
          callbacks.each { |c| chain.delete(c) }
          target.set_callbacks name, chain
        end

        self.set_callbacks name, callbacks.dup.clear
      end