nixos/budgie: Drop qt style override

https://hydra.nixos.org/build/295225429

This unbreaks nixosTests.budgie when a fix for qt6gtk2 is still in
review. This does not seem to work in Wayland so I guess we will
eventually drop that in next Budgie bump anyway.

See also 7e685d3693 for Cinnamon and 36bc3f46ba for Pantheon.

nixos/modules/services/x11/desktop-managers/budgie.nix

@@ -199,13 +199,6 @@ in
       monospace = mkDefault [ "Hack" ];
     };
 
-    # Qt application style.
-    qt = {
-      enable = mkDefault true;
-      style = mkDefault "gtk2";
-      platformTheme = mkDefault "gtk2";
-    };
-
     environment.pathsToLink = [
       "/share" # TODO: https://github.com/NixOS/nixpkgs/issues/47173
     ];