kwin: drop gcc12stdenv on aarch64 hack

pkgs/desktops/plasma-5/default.nix

@@ -110,7 +110,7 @@ let
                 broken = meta.broken or broken;
               };
           in
-          (args.stdenv or qtStdenv).mkDerivation (args // {
+          qtStdenv.mkDerivation (args // {
             inherit pname version meta outputs setupHook src nativeBuildInputs;
           });
       };

pkgs/desktops/plasma-5/kwin/default.nix

@@ -1,5 +1,4 @@
 { mkDerivation
-, stdenv
 , lib
 , extra-cmake-modules
 , kdoctools
@@ -57,7 +56,6 @@
 , plasma-framework
 , libqaccessibilityclient
 , python3
-, gcc12Stdenv
 }:
 
 # TODO (ttuegel): investigate qmlplugindump failure
@@ -145,12 +143,9 @@ mkDerivation {
     })
   ];
 
-  stdenv = if stdenv.isAarch64 then gcc12Stdenv else stdenv;
-
   CXXFLAGS = [
     ''-DNIXPKGS_XWAYLAND=\"${lib.getBin xwayland}/bin/Xwayland\"''
-  ]
-  ++ lib.optional stdenv.isAarch64 "-mno-outline-atomics";
+  ];
 
   postInstall = ''
     # Some package(s) refer to these service types by the wrong name.