Random bits of cleanup

[kocolosk]

Overview

I had forgotten to update mix.lock on a recent change to include support for Elixir v1.12, so that's included here. I also removed a few scripts that are leftovers from old build systems.

[kocolosk]

Hah, looks like the build system expects a bin directory to exist, but I just removed all the version-controlled files from that directory. Will see if it makes sense to mkdir -p there.

[nickva]

+1

mkdir -p before copying rebar or other files or a .keep file in to handle bin would work, whichever looks better overall.

[kocolosk]

Good thought on the .keep file, I added that for now. I feel like there's still some duplication and overlap between the bin/, build-aux/ and support/, but not going to try to resolve that here so taking the most conservative approach.