Drop dependencies and config for unused ports

@fdanis reports:

with apertis-v2020pre-package-builder, when I try to install the build dependencies for binutils it fails with:

gcc-8-cross-base-ports (= 8.3.0-2bzc1cross2) but 8.3.0-6bv2020dev0b1cross2 is to be installed

Since we don’t build this package anymore, we need to remove support for all Debian ports and otherwise unused architectures.