btrfs: remove useless comment from btrfs_pin_extent_for_log_replay()

The comment on top of btrfs_pin_extent_for_log_replay() mentioning that
the function must be called within a transaction is pointless as of
commit 9fce5704 ("btrfs: Make btrfs_pin_extent_for_log_replay take
transaction handle"), since the function now takes a transaction handle
as its first argument. So remove the comment because it's completely
useless now.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -2566,9 +2566,6 @@ int btrfs_pin_extent(struct btrfs_trans_handle *trans,
 	return 0;
 }
 
-/*
- * this function must be called within transaction
- */
 int btrfs_pin_extent_for_log_replay(struct btrfs_trans_handle *trans,
 				    const struct extent_buffer *eb)
 {