restorer: remove always true `has_futex' arg

Check for presence of robust futex list is in the reality
(futex_rla_len != 0).

That does code on dumping, in get_task_futex_robust_list():
> ret = syscall(SYS_get_robust_list, pid, &head, &len);
> if (ret < 0 && errno == ENOSYS) {
[..]
> 	len = 0;
[..]
> }
[..]
> info->futex_rla_len	= (u32)len;

And in images: futex_rla_len == 0 means that futex is not present.

So, we don't need additional restorer's parameter `has_futex'
which is always true, remove it.
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-restore.c

@@ -3237,7 +3237,6 @@ static int sigreturn_restore(pid_t pid, struct task_restore_args *task_args, uns
 
 		rst_reloc_creds(&thread_args[i], &creds_pos_next);
 
-		thread_args[i].has_futex	= true;
 		thread_args[i].futex_rla	= tcore->thread_core->futex_rla;
 		thread_args[i].futex_rla_len	= tcore->thread_core->futex_rla_len;
 		thread_args[i].pdeath_sig	= tcore->thread_core->pdeath_sig;

criu/include/restorer.h

@@ -82,7 +82,6 @@ struct thread_restore_args {
 	UserRegsEntry			gpregs;
 	u64				clear_tid_addr;
 
-	bool				has_futex;
 	u64				futex_rla;
 	u32				futex_rla_len;
 

criu/pie/restorer.c

@@ -426,7 +426,7 @@ static int restore_thread_common(struct thread_restore_args *args)
 {
 	sys_set_tid_address((int *)decode_pointer(args->clear_tid_addr));
 
-	if (args->has_futex && args->futex_rla_len) {
+	if (args->futex_rla_len) {
 		int ret;
 
 		ret = sys_set_robust_list(decode_pointer(args->futex_rla),