--- delete(val)
--- delete(val) { ... }

    val  == Ǥ򤹤٤Ƽޤ
    val ǤĤäϡ((*val*)) ֤ޤ

    valǤʤ nil ֤ޤ֥å
    ꤵƤХ֥åɾƤη̤֤ޤ

    :

        array = [1, 2, 3, 2, 1]
        p array.delete(2)       #=> 2
        p array                 #=> [1, 3, 1]

        # ֥åʤΰ nil ϤȤͤ
        # Ԥ줿ɤȽ򤹤뤳ȤϤǤʤ
        ary = [nil,nil,nil]
        p ary.delete(nil)       #=> nil
        p ary                   #=> []
        p ary.delete(nil)       #=> nil

