Reference the stockholm packages we still use through
stockholm.packages.<system> instead of its overlay.

nixpkgs' pkgs.writers replaces nix-writers' top-level writeDash,
writeDashBin, writeBashBin and write (now linkFarm).

Nothing uses them; red-host reads the clan vars secretLocation directly.

Copied from stockholm krebs/3modules/realwallpaper.nix (cc283503); the
wallpaper generator comes from stockholm's packages output instead of
its overlay.

Copied from stockholm krebs/3modules/reaktor2.nix (cc283503). The bot
itself goes to pkgs/reaktor2 (with blessings, which nixpkgs lacks),
since stockholm's packages output does not include it.

Copied from stockholm krebs/3modules/htgen.nix (cc283503), so it no
longer needs pkgs.htgen from the stockholm overlay.