reduce build dependencies

[spencersevilla]

"make build_deps" apt-gets all the necessary build packages; unfortunately this is almost 800MB of packages. I have a strong hunch that the majority of these packages are simple holdovers from prior features/code re-archs and actually aren't necessary to build the code right now. Someone needs to wade through this set of packages and axe the ones that aren't actually necessary.

Ideally, we get the dependencies down small enough that it's not a huge issue, at which point we can simply include "build_deps" as a target of "all", so that "make all" succeeds. The reason I don't do this right now is that it feels super shitty to just automatically download that much content onto someone's machine.