nixos/pantheon: enable power-profiles-daemon

switchboard-plug-power is providing support for this since 2.7.0.

Note that we don't handle the conflict with tlp because we have
no way of knowing which way a user wants to resolve the conflict.

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

@@ -136,6 +136,7 @@ in
       services.colord.enable = mkDefault true;
       services.fwupd.enable = mkDefault true;
       services.packagekit.enable = mkDefault true;
+      services.power-profiles-daemon.enable = mkDefault true;
       services.touchegg.enable = mkDefault true;
       services.touchegg.package = pkgs.pantheon.touchegg;
       services.tumbler.enable = mkDefault true;