Simplify the multiarch docker build

Make the binaries build run on the self-hosted runners

misc/docker-arch-to-rust-target.sh

@@ -1,15 +0,0 @@
-#!/bin/sh
-
-if [ "$#" -ne 1 ]; then
-  echo "usage: $0 [platform]" >&2
-  exit 1
-fi
-
-if [ "$1" = "linux/arm64" ] || [ "$1" = "linux/arm64/v8" ]; then
-  echo "aarch64-unknown-linux-musl"
-elif [ "$1" = "linux/amd64" ]; then
-  echo "x86_64-unknown-linux-musl"
-else
-  echo "unsupported platform $1" >&2
-  exit 2
-fi