usr.sbin/makefs: Fix "-o D" option when intermediate directories exist

usr.sbin/makefs: Fix "-o D" option when intermediate directories exist

HAMMER2_DELETE_FILE assumes a given inode is a directory containing
dirent whose name is destroy.path. Therefore ioctl caller side needs
to split path components and only pass the last component along with
its direct parent directory inode.

It currently worked only when a target file path is the last component
without intermediate directories (no intermediate '/').

hammer2_ioc_destroy_t::path should be renamed to "name", as it
doesn't allow a file "path".