go-ethereum: Dont install sources in $out

pkgs/applications/altcoins/go-ethereum.nix

···
   # Fixes Cgo related build failures (see https://github.com/NixOS/nixpkgs/issues/25959 )
   hardeningDisable = [ "fortify" ];
 
+  # Only install binaries in $out, source is not interesting and takes ~50M
+  outputs = [ "out" ];
+  preFixup = ''
+    export bin="''${out}"
+  '';
+  installPhase = ''
+    mkdir -p $out/bin $out
+    dir="$NIX_BUILD_TOP/go/bin"
+    [ -e "$dir" ] && cp -r $dir $out
+  '';
+
   src = fetchFromGitHub {
     owner = "ethereum";
     repo = "go-ethereum";