um: make copy_sc() static

... and kill it in amd64 - not used.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/sys-i386/signal.c b/arch/um/sys-i386/signal.c
index 4403b48..b87195b 100644
--- a/arch/um/sys-i386/signal.c
+++ b/arch/um/sys-i386/signal.c
@@ -10,7 +10,7 @@
 #include "frame_kern.h"
 #include "skas.h"
 
-void copy_sc(struct uml_pt_regs *regs, void *from)
+static void copy_sc(struct uml_pt_regs *regs, void *from)
 {
 	struct sigcontext *sc = from;