No longer need to be stored on disk, can be simulated on
the chip side. As mentioned in other commits, the parent
entries had dozens of problems with atomic updates, as
well as making everything just a bit more complex than
is needed.
Removing the dependency to the parent pointer solves
many issues with non-atomic updates of children's
parent pointers with respect to any move operations.
However, this comes with an embarrassingly terrible
runtime as the only other option is to exhaustively
check every dir entry to find a child's parent.
Fortunately, deorphaning should be a relatively rare
operation.
