server-info: use strbuf to read old info/packs file

server-info: use strbuf to read old info/packs file

This old code uses fgets with a fixed-size buffer. Let's use a strbuf
instead, so we don't have to wonder if "1000" is big enough, or what
happens if we see a long line.

This also lets us drop our custom code to trim the newline.

Probably nobody actually cares about the 1000-char limit (after all, the
lines generally only say "P pack-[0-9a-f]{40}.pack"), so this is mostly
just about cleanup/readability.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>