chore: remove unused overlays

overlays/default/firebird-emu.nix

@@ -1 +0,0 @@
-import ./firebird-emu/default.nix

overlays/default/firebird-emu/default.nix

@@ -1,3 +0,0 @@
-self: super: {
-  firebird-emu = self.libsForQt5.callPackage ./package.nix {};
-}

overlays/default/firebird-emu/package.nix

@@ -1,44 +0,0 @@
-{
-  stdenv,
-  lib,
-  fetchFromGitHub,
-  qmake,
-  qtbase,
-  qtdeclarative,
-  qtquickcontrols,
-  wrapQtAppsHook,
-}:
-stdenv.mkDerivation rec {
-  pname = "firebird-emu";
-  version = "1.6";
-
-  src = fetchFromGitHub {
-    owner = "nspire-emus";
-    repo = "firebird";
-    rev = "v${version}";
-    fetchSubmodules = true;
-    hash = "sha256-ZptjlnOiF+hKuKYvBFJL95H5YQuR99d4biOco/MVEmE=";
-  };
-
-  NIX_CFLAGS_COMPILE = lib.optionals (stdenv.cc.isClang && stdenv.isDarwin) [
-    "-fno-lto" # work around https://github.com/NixOS/nixpkgs/issues/19098
-  ];
-
-  nativeBuildInputs = [qmake wrapQtAppsHook];
-
-  buildInputs = [qtbase qtdeclarative qtquickcontrols];
-
-  postInstall = lib.optionalString stdenv.hostPlatform.isDarwin ''
-    mkdir $out/Applications
-    mv $out/bin/${pname}.app $out/Applications/
-  '';
-
-  meta = {
-    homepage = "https://github.com/nspire-emus/firebird";
-    description = "Third-party multi-platform emulator of the ARM-based TI-Nspire™ calculators";
-    license = lib.licenses.gpl3;
-    maintainers = with lib.maintainers; [pneumaticat];
-    # Only tested on Linux, but likely possible to build on, e.g. macOS
-    platforms = lib.platforms.unix;
-  };
-}

overlays/default/paperwm.nix

@@ -1,15 +0,0 @@
-self: super: {
-  gnomeExtensions =
-    super.gnomeExtensions
-    // {
-      paperwm = super.gnomeExtensions.paperwm.overrideDerivation (old: {
-        version = "43.0";
-        src = super.fetchFromGitHub {
-          owner = "paperwm";
-          repo = "PaperWM";
-          rev = "64960df6cde10bcf47c33ce56a2d35e99d8d02bf";
-          sha256 = "sha256-ejyWIa4HX1lEIHc9qax8jgrgi992W6rkTK60FGzKI/E=";
-        };
-      });
-    };
-}

overlays/iptables/default.nix

@@ -1,5 +0,0 @@
-self: super: {
-  iptables = super.iptables.override {
-    nftablesCompat = false;
-  };
-}