Decommission bugs.archlinux.org and replace it with a static copy[1]

As announced[2][3] the bugtracker has been migrated to gitlab, so
bugs.a.o can be decommissioned and replaced with a static copy[1](to
avoid link rot).

[1] https://gitlab.archlinux.org/archlinux/bugs-archive/
[2] https://archlinux.org/news/bugtracker-migration-to-gitlab-completed/
[3] https://lists.archlinux.org/hyperkitty/list/arch-dev-public@lists.archlinux.org/thread/WYXDTJ3TR2DWRQCDZK44BQDH67IDVGTS/

Fix #550
Fix #551