feat(db-functions): Check the archive index in check_reproducible

With the archive and repos no longer hosted on the same server[1], the
existence of "dependent packages" can no longer be determined solely by
checking whether the file exists in the local archive directory, which
now contains at most a few days worth of packages.

To solve this the archive index[2] must also be checked which contains
all archived packages. We still need to check locally first, as the
archive index is only updated once a day.

[1] https://lists.archlinux.org/archives/list/arch-dev-public@lists.archlinux.org/thread/B66SQUW4HOJAN2WHG4RLEBLYWNWOSF3Y/
[2] https://archive.archlinux.org/packages/.all/index.0.xz