Remove unused macro in preempt support

Index: linux/arch/x86_64/kernel/entry.S
===================================================================
--- linux.orig/arch/x86_64/kernel/entry.S
+++ linux/arch/x86_64/kernel/entry.S
@@ -44,10 +44,7 @@
 
 	.code64
 
-#ifdef CONFIG_PREEMPT
-#define preempt_stop cli
-#else
-#define preempt_stop
+#ifndef CONFIG_PREEMPT
 #define retint_kernel retint_restore_args
 #define paranoid_exit_kernel paranoid_restore
 #endif