The httpredir.debian.org service has been discontinued in favour of
deb.debian.org and httpredir.debian.org now redirects to deb.debian.org.

https://lists.debian.org/debian-mirrors/2017/02/msg00000.html
https://wiki.debian.org/DebianGeoMirror#httpredir.debian.org_.2F_http.debian.net

Cf. https://bugs.debian.org/872719Signed-off-by: Salvatore Bonaccorso <carnil@debian.org>