Prior to v1.5.4~14, expire_reflog() had to be an each_ref_fn because
it was passed to for_each_reflog(). Since then, there has been no
reason for it to implement the each_ref_fn interface. So...
* Remove the "unused" parameter (which took the place of "flags", but
was really unused).
* Declare the last parameter to be (struct cmd_reflog_expire_cb *)
rather than (void *).
Helped-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>