csky: Remove kernel_thread declaration

Remove csky's kernel_thread declaration because it's not needed.

Signed-off-by: Mike Christie <[e-mail]>
Acked-by: Michael S. Tsirkin <[e-mail]>
Signed-off-by: Christian Brauner (Microsoft) <[e-mail]>

arch/csky/include/asm/processor.h

···
 /* Prepare to copy thread state - unlazy all lazy status */
 #define prepare_to_copy(tsk)    do { } while (0)
 
-extern int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
-
 unsigned long __get_wchan(struct task_struct *p);
 
 #define KSTK_EIP(tsk)		(task_pt_regs(tsk)->pc)