make uname actually set sysname to Plan9 if no /env/osname exists.

Reference: /n/sources/patch/applied/uname-sysname
Date: Thu Mar 30 03:38:22 CES 2006
Signed-off-by: geoff@collyer.net

--- /sys/src/ape/lib/ap/plan9/uname.c	Thu Mar 30 03:37:56 2006
+++ /sys/src/ape/lib/ap/plan9/uname.c	Thu Mar 30 03:37:54 2006
@@ -5,11 +5,9 @@
 int
 uname(struct utsname *n)
 {
-	char *osname;
-	
 	n->sysname = getenv("osname");
 	if(!n->sysname)
-		osname = "Plan9";
+		n->sysname = "Plan9";
 	n->nodename = getenv("sysname");
 	if(!n->nodename){
 		n->nodename = getenv("site");