Don't reject HOT_REMOVE_DISK request for an array that is not yet started.

There is really no need for this test here, and there are valid
cases for selectively removing devices from an array that
it not actually active.
Signed-off-by: Neil Brown <neilb@suse.de>

drivers/md/md.c

@@ -4300,9 +4300,6 @@ static int hot_remove_disk(mddev_t * mddev, dev_t dev)
 	char b[BDEVNAME_SIZE];
 	mdk_rdev_t *rdev;
 
-	if (!mddev->pers)
-		return -ENODEV;
-
 	rdev = find_rdev(mddev, dev);
 	if (!rdev)
 		return -ENXIO;