cachefiles: remove unused macro list_to_page()

Signed-off-by: Haicheng Li <haicheng.li@linux.intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-By: Milosz Tanski <milosz@adfin.com>
Acked-by: Jeff Layton <jlayton@redhat.com>