promisor-remote: keep accepted promisor_info structs alive

promisor-remote: keep accepted promisor_info structs alive

In filter_promisor_remote(), the instances of `struct promisor_info`
for accepted remotes are dismantled into separate parallel data
structures (the 'accepted' strvec for server names, and
'accepted_filters' for filter strings) and then immediately freed.

Instead, let's keep these instances on an 'accepted_remotes' list.

This way the post-loop phase can iterate a single list to build the
protocol reply, apply advertised filters, and mark remotes as
accepted, rather than iterating three separate structures.

This refactoring also prepares for a future commit that will add a
'local_name' member to 'struct promisor_info'. Since struct instances
stay alive, downstream code will be able to simply read both names
from them rather than needing yet another parallel strvec.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>