delete xns.  we no longer have an xns library or header file

Reference: /n/atom/patch/applied2013/snoopynoxns
Date: Fri Oct 25 01:46:59 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ip/snoopy/mkfile	Fri Oct 25 01:46:45 2013
+++ /sys/src/cmd/ip/snoopy/mkfile	Fri Oct 25 01:46:45 2013
@@ -43,11 +43,11 @@
 	tcp\
 	ttls\
 	udp\
-	xns\
-	xnsecho\
-	xnserror\
-	xnsroute\
-	xnsspp\
+#	xns\
+#	xnsecho\
+#	xnserror\
+#	xnsroute\
+#	xnsspp\
 
 POBJS=${PROTOS:%=%.$O}