Rename expire_reflog_cb to expire_reflog_policy_cb
This is the first step towards separating the data needed by the
policy code from the data needed by the reflog expiration machinery.
(In a moment we will add a *new* "struct expire_reflog_cb" for the use
of expire_reflog() itself, then move fields selectively from
expire_reflog_policy_cb to expire_reflog_cb.)
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>