ceph: remove incorrect and unused CEPH_INO_DOTDOT macro

Ceph have removed this macro and the 0x3 will be use for global dummy
snaprealm.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>