rst: Remove threads restore serialization

This thing was introduced by 01f8f8f4 to help not mixing
per-thread error messages in log files. Now messages are
not mixed by other means, so this thing is useless.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -2372,8 +2372,6 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core)
 	if (ret < 0)
 		goto err;
 
-	mutex_init(&task_args->rst_lock);
-
 	/*
 	 * Now prepare run-time data for threads restore.
 	 */

include/restorer.h

@@ -108,8 +108,6 @@ struct task_restore_core_args {
 	int				logfd;
 	unsigned int			loglevel;
 
-	mutex_t				rst_lock;
-
 	/* threads restoration */
 	int				nr_threads;		/* number of threads */
 	int				nr_zombies;

pie/restorer.c

@@ -286,8 +286,6 @@ long __export_restore_thread(struct thread_restore_args *args)
 	if (restore_thread_common(rt_sigframe, args))
 		goto core_restore_end;
 
-	mutex_unlock(&args->ta->rst_lock);
-
 	ret = restore_creds(&args->ta->creds);
 	if (ret)
 		goto core_restore_end;
@@ -817,8 +815,6 @@ long __export_restore_task(struct task_restore_core_args *args)
 			if (thread_args[i].pid == args->t->pid)
 				continue;
 
-			mutex_lock(&args->rst_lock);
-
 			new_sp =
 				RESTORE_ALIGN_STACK((long)thread_args[i].mem_zone.stack,
 						    sizeof(thread_args[i].mem_zone.stack));