Build dynamic tezos binaries via nix

Problem: Rust doesn't work well with musl on nix, see
NixOS/nixpkgs#71195.

Solution: Build dynamic binaries instead. It's fine since these
binaries aren't used in the releases and used only in our
internal infrastructure.

nix/default.nix

@@ -12,7 +12,7 @@ let
     (import ./build/release-binaries.nix);
   binaries = builtins.listToAttrs (map (meta: {
     inherit (meta) name;
-    value = bin pkgs.pkgsMusl.ocamlPackages.${meta.name} // { inherit meta; };
+    value = bin pkgs.ocamlPackages.${meta.name} // { inherit meta; };
   }) release-binaries);
 
   # Bundle the contents of a package set together, leaving the original attrs intact