osbuilder: Remove musl installations

Remove a lot of cruft of musl installations -- we needed those for the
Go agent, but Rustup just takes care of everything. aarch64 on
Debian-based & Alpine is an exception -- create a symlink
`aarch64-linux-musl-gcc` to `musl-tools`'s `musl-gcc` or `gcc` on
Alpine. This is unified -- arch-specific Dockerfiles are removed.

Furthermore, we should keep it in Ubuntu for supporting the offline SEV
KBC. We also keep it in Clear Linux, as that runs our internal checks,
but it is e.g. not shipped in CentOS Stream 9.

Signed-off-by: Jakob Naucke <jakob.naucke@ibm.com>

ci/install_musl.sh

@@ -1,24 +0,0 @@
-#!/usr/bin/env bash
-# Copyright (c) 2020 Ant Group
-#
-# SPDX-License-Identifier: Apache-2.0
-#
-
-set -e
-
-install_aarch64_musl() {
-	local arch=$(uname -m)
-	if [ "${arch}" == "aarch64" ]; then
-		local musl_tar="${arch}-linux-musl-native.tgz"
-		local musl_dir="${arch}-linux-musl-native"
-		pushd /tmp
-		if curl -sLO --fail https://musl.cc/${musl_tar}; then
-			tar -zxf ${musl_tar}
-			mkdir -p /usr/local/musl/
-			cp -r ${musl_dir}/* /usr/local/musl/
-		fi
-		popd
-	fi
-}
-
-install_aarch64_musl