Remove supertype->devfd

It is never used.

mdadm.h

@@ -452,7 +452,6 @@ struct supertype {
 
 	/* extra stuff used by mdmon */
 	struct active_array *arrays;
-	int devfd;
 	int sock; /* listen to external programs */
 	int mgr_pipe[2]; /* communicate between threads */
 	int mon_pipe[2]; /* communicate between threads */

mdmon.c

@@ -196,7 +196,6 @@ int main(int argc, char *argv[])
 	/* hopefully it is a container - we'll check later */
 
 	container = malloc(sizeof(*container));
-	container->devfd = mdfd;
 	container->devnum = fd2devnum(mdfd);
 	container->devname = devnum2devname(container->devnum);
 
@@ -269,6 +268,7 @@ int main(int argc, char *argv[])
 		exit(3);
 	}
 
+	close(mdfd);
 
 	mlockall(MCL_FUTURE);