x86: Remove duplicated #include

Remove duplicated #include in:

  arch/x86/kernel/dumpstack.c

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index c8405718..2d8a371 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -15,7 +15,6 @@
 #include <linux/bug.h>
 #include <linux/nmi.h>
 #include <linux/sysfs.h>
-#include <linux/ftrace.h>
 
 #include <asm/stacktrace.h>