rather than performing apt-get update multiple times which is rather slo...

...w, use a function, set a flag, so we only apt-get update a single time

use --no-install-recommends to keep the dependencies set smaller

note - I have some more related stuff to add. But https://github.com/petrockblog/RetroPie-Setup/pull/369 needs to be pulled first. Once it is, I can de-duplicate both the retropie setup/packages script, moving some stuff to the helpers file, and rework the core dependency function to include gcc-4.7 as it is the default compiler.