fix warning

Reference: /n/atom/patch/applied/dnsmainnit
Date: Sun Aug 16 00:13:19 CES 2015
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ndb/dns.c	Sun Aug 16 00:13:21 2015
+++ /sys/src/cmd/ndb/dns.c	Sun Aug 16 00:13:22 2015
@@ -121,7 +121,6 @@
 {
 	int kid, pid;
 	char servefile[Maxpath], ext[Maxpath];
-	Dir *dir;
 
 	setnetmtpt(mntpt, sizeof mntpt, nil);
 	ext[0] = 0;