Refactored deduplicate/deorphan step to single deorphan step

Deduplication and deorphan steps aren't required under indentical
conditions, but they can be processed in the same iteration of the
filesystem. Since lfs_alloc (requires deorphan) occurs on most write
calls to the filesystem (requires deduplication), it was simpler to
just compine the steps into a single lfs_deorphan step.

Also traded out the places where lfs_rename/lfs_remove just defer
operations to the deorphan step. This adds a bit of code, but also
significantly speeds up directory operations.