staging: ktap: remove unused <asm/syscall.h> header file

Fengguang Wu reported that ktap compile failed in mips,
the reason is it cannot found <asm/syscall.h> in mips arch.

Due to the code serviced by <asm/syscall.h> already removed,
so just simply remove the according header file to avoid
compiler failure.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ktap/interpreter/library/kdebug.c

@@ -23,7 +23,6 @@
 #include <linux/ctype.h>
 #include <linux/version.h>
 #include <linux/ftrace_event.h>
-#include <asm/syscall.h> //syscall_set_return_value defined here
 #include "../../include/ktap.h"
 
 static void ktap_call_probe_closure(ktap_state *mainthread, ktap_closure *cl,