um: remove unused smp_sigio_handler() declaration

This function doesn't exist, remove its declaration.

Signed-off-by: Johannes Berg <[e-mail]>
Acked-By: Anton Ivanov <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

arch/um/include/shared/kern_util.h

···
 			     int is_write, int is_user, int *code_out);
 
 extern unsigned int do_IRQ(int irq, struct uml_pt_regs *regs);
-extern int smp_sigio_handler(void);
 extern void initial_thread_cb(void (*proc)(void *), void *arg);
 extern int is_syscall(unsigned long addr);