Lean

This is a stab at removing everything under buildroot, which is replaced by downloading (or using an existing SteamOSInstaller.zip). This makes the git repository much smaller, and keeps everything that's modified in one place so you don't have to look through the repo to figure out new debs. This should allow allow for easier porting in the future with the SteamOSInstaller.zip is updated and gen.sh can drop just be dropped in.

Everything seems to work properly when running gen.sh with the exception of building the ISO. Need to figure out what the error is exactly, but this is a good POC for stripping many of the redundant binary files out of the repo.