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.

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

versions.yaml

@@ -233,19 +233,6 @@ externals:
       .*/v?(\d\S+)\.tar\.gz
     version: "v1.0.1"
 
-  musl:
-    description: |
-      The musl library is used to build the rust agent.
-    url: "https://www.musl-libc.org/"
-    uscan-url: >-
-      https://www.musl-libc.org/releases/
-      musl-([\d\.]+)\.tar\.gz
-    version: "1.1.23"
-    meta:
-      description: |
-        'newest-version' is the latest version known to work.
-      newest-version: "1.1.23"
-
   nydus:
     description: "Nydus image acceleration service"
     url: "https://github.com/dragonflyoss/image-service"