move min-list-garbage into min-collect-garbage pkg

we don't want it in the same package as min-copy-closure as
that depends on bash

pkgs/min-collect-garbage/default.nix

@@ -0,0 +1,17 @@
+{
+  stdenv
+, nix
+, cpio
+, openssh
+}: stdenv.mkDerivation {
+  name = "min-collect-garbage";
+  buildInputs = [ ];
+#  propagatedBuildInputs = [ openssh ];
+  src = ./.;
+  makeFlags = [ "min-list-garbage" ];
+  installPhase = ''
+    mkdir -p $out/bin
+    cp  min-collect-garbage.sh $out/bin/min-collect-garbage
+    cp min-list-garbage $out/bin
+  '';
+}