Moving off of scionlabs scion fork and matching scion reqs for go 1.21

Exclude testing and misc pkgs from the drv build.

Removing scion.sh from pkg scion as its a wrapper on very specific
tools and testing processes within the scion repo. It doesnt seem
very useful to include as a pkg required for operating a scion router.

ignoring _examples in the build of scion-apps and moving that to a
separate pkg.

scionlab uses a fork of upstream scion which is pretty old. Its also a
completely custom environment that at this time doesnt seem like its
worth replicating in this flake.