The inode since ioctl was the last user of the btree. It doesn't yet
work because the item cache doesn't know how to search for items by
sequence yet.
It's not yet clear exactly how we'll build the data since ioctls. It'll
be easy enough to refactor the inode since item walk if they follow a
similar pattern again.
Signed-off-by: Zach Brown <zab@versity.com>