um: Remove broken SMP support

At times where UML used the TT mode to operate it had
kind of SMP support. It never got finished nor was
stable.
Let's rip out that cruft and stop confusing developers
which do tree-wide SMP cleanups.

If someone wants SMP support UML it has do be done from scratch.

Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/kernel/process.c

@@ -259,17 +259,6 @@ int strlen_user_proc(char __user *str)
 	return strlen_user(str);
 }
 
-int smp_sigio_handler(void)
-{
-#ifdef CONFIG_SMP
-	int cpu = current_thread_info()->cpu;
-	IPI_handler(cpu);
-	if (cpu != 0)
-		return 1;
-#endif
-	return 0;
-}
-
 int cpu(void)
 {
 	return current_thread_info()->cpu;