criu: Remove parent-img service fd

It's no longer needed. All parent manipulations are done in-place
using CR_PARENT_LINK name.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

image.c

@@ -244,26 +244,14 @@ int open_image_dir(char *dir)
 	fd = ret;
 
 	if (opts.img_parent) {
-		int pfd;
-
 		ret = symlinkat(opts.img_parent, fd, CR_PARENT_LINK);
-		if (ret < 0) {
+		if (ret < 0 && errno != EEXIST) {
 			pr_perror("Can't link parent snapshot");
 			goto err;
 		}
-
-		pfd = openat(fd, CR_PARENT_LINK, O_RDONLY);
-		if (pfd < 0) {
-			pr_perror("Can't open parent snapshot");
-			goto err;
 	}
 
-		ret = install_service_fd(PARENT_FD_OFF, pfd);
-
-		close(pfd);
-	}
-
-	return ret;
+	return 0;
 
 err:
 	close_image_dir();

include/servicefd.h

@@ -11,7 +11,6 @@ enum sfd_type {
 	PROC_FD_OFF,	/* fd with /proc for all proc_ calls */
 	CTL_TTY_OFF,
 	SELF_STDIN_OFF,
-	PARENT_FD_OFF,
 	CR_PROC_FD_OFF, /* some other's proc fd.
 			 *  For dump -- target ns' proc
 			 *  For restore -- CRIU ns' proc