This backs out commit 89d57ffb29577c99f0f5187b76bff369f19c5886.
This is causing a CI failure because we can't build musl binaries,
presumably because the rust-toolchain file overriding the chosen
musl toolchain for some reason. Backout until we can reapply
a proper fix.
Signed-off-by: Austin Seipp <aseipp@pobox.com>