treewide: load structured attributes in all bash builders consistently

It's hard to put the sourcing of ./.attrs.sh into all builder
consistently - mistakes will happen. Thus, load structured attrs once in
make-derivation and then source the remaining builder on top.

This should fix quite a few builders with structured attributes in
principle. Most importantly it helps substitute / substituteAll, which
are required for bootstrap on some platforms.

nixos/modules/services/computing/slurm/slurm.nix

@@ -331,7 +331,6 @@ in
         name = "wrappedSlurm";
 
         builder = pkgs.writeText "builder.sh" ''
-          source $stdenv/setup
           mkdir -p $out/bin
           find  ${lib.getBin cfg.package}/bin -type f -executable | while read EXE
           do