nixos/cinnamon: Do not set QT_QPA_PLATFORMTHEME

Mint no longer ships qt5ct since Mint 22 and no longer ships a
qt5ct.conf in Mint 22.1. Following their changes I think we will
also drop our override and delegate the decision to user. Also
the gtk2 platform theme actually depends on gtk2.

f239cde908

nixos/doc/manual/release-notes/rl-2505.section.md

@@ -109,7 +109,8 @@
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
-- Cinnamon has been updated to 6.4.
+- Cinnamon has been updated to 6.4, please check the [upstream announcement](https://www.linuxmint.com/rel_xia_whatsnew.php) for more details.
+  - Following [changes in Mint 22](https://github.com/linuxmint/mintupgrade/commit/f239cde908288b8c250f938e7311c7ffbc16bd59) we are no longer overriding Qt application styles. You can still restore the previous default with `qt.style = "gtk2"` and `qt.platformTheme = "gtk2"`.
 
 - `networking.wireguard` now has an optional networkd backend. It is enabled by default when `networking.useNetworkd` is enabled, and it can be enabled alongside scripted networking with `networking.wireguard.useNetworkd`. Some `networking.wireguard` options have slightly different behavior with the networkd and script-based backends, documented in each option. Before upgrading, make sure the `privateKeyFile` and `presharedKeyFile` paths are readable by the `systemd-network` user if using the networkd backend.
 

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

@@ -220,13 +220,6 @@ in
       programs.bash.vteIntegration = mkDefault true;
       programs.zsh.vteIntegration = mkDefault true;
 
-      # Qt application style
-      qt = {
-        enable = mkDefault true;
-        style = mkDefault "gtk2";
-        platformTheme = mkDefault "gtk2";
-      };
-
       # Default Fonts
       fonts.packages = with pkgs; [
         dejavu_fonts # Default monospace font in LMDE 6+