Kconfig: remove dangling references to the deleted file

Commit 202dc3fc (Documentation: remove
obsolete networking/multicast.txt file) deleted the obsolete file. After
the file has been removed, clean up a couple of places where references
to the deleted file were made so that users wouldn't be confused when
they consult the Help menu.
Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -9,10 +9,7 @@ config IP_MULTICAST
 	  intend to participate in the MBONE, a high bandwidth network on top
 	  of the Internet which carries audio and video broadcasts. More
 	  information about the MBONE is on the WWW at
-	  <http://www.savetz.com/mbone/>. Information about the multicast
-	  capabilities of the various network cards is contained in
-	  <file:Documentation/networking/multicast.txt>. For most people, it's
-	  safe to say N.
+	  <http://www.savetz.com/mbone/>. For most people, it's safe to say N.
 
 config IP_ADVANCED_ROUTER
 	bool "IP: advanced router"
@@ -223,10 +220,8 @@ config IP_MROUTE
 	  packets that have several destination addresses. It is needed on the
 	  MBONE, a high bandwidth network on top of the Internet which carries
 	  audio and video broadcasts. In order to do that, you would most
-	  likely run the program mrouted. Information about the multicast
-	  capabilities of the various network cards is contained in
-	  <file:Documentation/networking/multicast.txt>. If you haven't heard
-	  about it, you don't need it.
+	  likely run the program mrouted. If you haven't heard about it, you
+	  don't need it.
 
 config IP_MROUTE_MULTIPLE_TABLES
 	bool "IP: multicast policy routing"