linux-headers: Remove dead old version

This sat around unused for who knows how long

pkgs/os-specific/linux/kernel-headers/default.nix

@@ -1,29 +0,0 @@
-{ stdenv, kernel, perl
-, hostPlatform
-}:
-
-let
-  baseBuildFlags = [ "INSTALL_HDR_PATH=$(out)" "headers_install" ];
-in stdenv.mkDerivation {
-  name = "linux-headers-${kernel.version}";
-
-  inherit (kernel) src patches;
-
-  nativeBuildInputs = [ perl ];
-
-  buildFlags = [ "ARCH=${stdenv.platform.kernelArch}" ] ++ baseBuildFlags;
-
-  crossAttrs = {
-    inherit (kernel.crossDrv) src patches;
-    buildFlags = [ "ARCH=${hostPlatform.platform.kernelArch}" ] ++ baseBuildFlags;
-  };
-
-  installPhase = ''
-    find $out \( -name ..install.cmd -o -name .install \) -print0 | xargs -0 rm
-  '';
-
-  # Headers shouldn't reference anything else
-  allowedReferences = [];
-
-  meta.platforms = stdenv.lib.platforms.linux;
-}