net: Remove references to wan-router.txt in Kconfigs

This patch removes references in drivers/net/wan/Kconfig and
net/wanrouter/Kconfig to Documentation/networking/wan-router.txt
which was removed in commit 99971e70
("[WANPIPE]: Forgotten bits of Sangoma drivers removal.").
Signed-off-by: NJohann Felix Soden <johfel@users.sourceforge.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/wan/Kconfig

@@ -390,8 +390,7 @@ config WAN_ROUTER_DRIVERS
 
 	  Select driver your card and remember to say Y to "Wan Router."
 	  You will need the wan-tools package which is available from
-	  <ftp://ftp.sangoma.com/>. For more information read:
-	  <file:Documentation/networking/wan-router.txt>.
+	  <ftp://ftp.sangoma.com/>.
 
 	  Note that the answer to this question won't directly affect the
 	  kernel except for how subordinate drivers may be built:

net/wanrouter/Kconfig

@@ -20,8 +20,6 @@ config WAN_ROUTER
 	  wish to use your Linux box as a WAN router, say Y here and also to
 	  the WAN driver for your card, below.  You will then need the
 	  wan-tools package which is available from <ftp://ftp.sangoma.com/>.
-	  Read <file:Documentation/networking/wan-router.txt> for more
-	  information.
 
 	  To compile WAN routing support as a module, choose M here: the
 	  module will be called wanrouter.