plasma-workspace: fix QtQuick style used by KCMs
plasma-workspace: fix QtQuick style used by KCMs

The KCMs now use the style provided by `qqc2-desktop-style` instead of
the default QtQuick one.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs