ipv6: kill two unused macro definition

1. IPV6_TLV_TEL_DST_SIZE
This has not been using for several years since created.

2. RT6_INFO_LEN
commit 33120b30 kill all RT6_INFO_LEN's references, but only this definition remained.

commit 33120b30
Author: Alexey Dobriyan <adobriyan@sw.ru>
Date:   Tue Nov 6 05:27:11 2007 -0800

    [IPV6]: Convert /proc/net/ipv6_route to seq_file interface

Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>