cd9660: Remove some unneeded definitions
- cd_ino_t can be dropped since ino_t is now 64 bits wide.
- ISOFSMNT_ROOT is unused (and defined only for the kernel).
No functional change intended.
Reviewed by: olce, imp, kib, emaste
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D47880