ALSA: seq: Remove superfluous snd_seq_queue_client_leave_cells() call

With the previous two fixes for the write / ioctl races:
  ALSA: seq: Don't allow resizing pool in use
  ALSA: seq: More protection for concurrent write and ioctl races
the cells aren't any longer in queues at the point calling
snd_seq_pool_done() in snd_seq_ioctl_set_client_pool().  Hence the
function call snd_seq_queue_client_leave_cells() can be dropped safely
from there.
Suggested-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_clientmgr.c

@@ -1846,7 +1846,6 @@ static int snd_seq_ioctl_set_client_pool(struct snd_seq_client *client,
 				return -EBUSY;
 			/* remove all existing cells */
 			snd_seq_pool_mark_closing(client->pool);
-			snd_seq_queue_client_leave_cells(client->number);
 			snd_seq_pool_done(client->pool);
 		}
 		client->pool->size = info->output_pool;