take it out of the mkfile too

Reference: /n/patches.lsub.org/patch/nosacmkfile
Date: Thu Jul  5 12:44:12 CES 2012
Signed-off-by: paurea@lsub.org

--- /sys/src/nix/mk/bootmkfile	Sat May 26 12:16:43 2012
+++ /sys/src/nix/mk/bootmkfile	Thu Jul  5 12:43:22 2012
@@ -10,7 +10,6 @@
 	local.$O\
 	embed.$O\
 	settime.$O\
-	sac.$O\
 	paq.$O\
 	printstub.$O\
 	parts.$O\