def remove_filter(name)
      defined.delete name.to_s.downcase
      if constants.map(&:to_s).include?(name.to_s)
        remove_const name.to_sym
      end
    end
def remove_filter(name)
      defined.delete name.to_s.downcase
      if constants.map(&:to_s).include?(name.to_s)
        remove_const name.to_sym
      end
    end
Removes a filter from Haml. If the filter was removed, it returns
 the Module that was removed upon success, or nil on failure. If you try
 to redefine a filter, Haml will raise an error. Use this method first to
 explicitly remove the filter before redefining it.
 @return Module The filter module that has been removed
 @since 4.0