ci: remove musl check

It requires installing Zig and slows down CI.
This was not broken for a while and we can do
more frequent core releases to catch problems.

.github/workflows/ci.yml

@@ -39,10 +39,6 @@ jobs:
       - name: Check
         run: cargo check --workspace --all-targets --all-features
 
-      # Check with musl libc target which is used for `deltachat-rpc-server` releases.
-      - name: Check musl
-        run: scripts/zig-musl-check.sh
-
   cargo_deny:
     name: cargo deny
     runs-on: ubuntu-latest