[PATCH] Remove duplicate file in Documentation/networking (drivers_net_wan_Kconfig)

wanpipe.txt and wan-router.txt in Documentation/networking contain the exact
same information (diff between the two shows no drivers/net/wan/Kconfig.

Signed-off-by: Tobias Klauser <tklauser@nuerscht.ch>
Signed-off-by: Domen Puncer <domen@coderock.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>