remove useless clean rule

Reference: /n/atom/patch/applied2013/aoedbfsmk
Date: Tue Jun 18 23:04:11 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/aoedbfs/mkfile	Tue Jun 18 23:04:03 2013
+++ /sys/src/cmd/aoedbfs/mkfile	Tue Jun 18 23:04:03 2013
@@ -9,6 +9,3 @@
 #HFILES=none
 
 </sys/src/cmd/mkone
-
-clean:
-	rm -f $O.out *.$O $TARG