--- delete_if {|key, value| ... }
--- reject! {|key, value| ... }

    key  value Ȥƥ֥åɾͤǤ
    Ǥ self ޤ

    delete_if Ͼ self ֤ޤ
    reject! ϡǤʤäˤ nil ֤
    Ǥʤ self ֤ޤ

