Cache_inode_read_conf: remove dead code

remove Symlink Expiration Time and Directory Expiration Time
and associated variables which aren't used

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
9P: Change op lookup array indexation to get function from code directly

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>