btrfs: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from btrfs.

Cc: Chris Mason <chris.mason@fusionio.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 8c6e61d..f2eb24c 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -100,10 +100,6 @@
 	fs_info->fs_state = BTRFS_SUPER_FLAG_ERROR;
 }
 
-/* NOTE:
- *	We move write_super stuff at umount in order to avoid deadlock
- *	for umount hold all lock.
- */
 static void save_error_info(struct btrfs_fs_info *fs_info)
 {
 	__save_error_info(fs_info);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b8708f9..e86ae04 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1744,10 +1744,6 @@
 
 	device->fs_devices = root->fs_info->fs_devices;
 
-	/*
-	 * we don't want write_supers to jump in here with our device
-	 * half setup
-	 */
 	mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
 	list_add_rcu(&device->dev_list, &root->fs_info->fs_devices->devices);
 	list_add(&device->dev_alloc_list,