hitagi: Disable corectrl

I renewed the thermal paste on its GPU and replaced the stock fan with
two Noctua NF-A9 PWM that are controlled via the mainboard’s fan headers
(connected via a Y splitter), so corectrl is no longer necessary.

machines/hitagi/configuration.nix

@@ -72,6 +72,4 @@
   networking.hostName = "hitagi";
 
   system.stateVersion = "20.03";
-
-  programs.corectrl.enable = true;
 }