linux_chromiumos_3_18: remove kernel due lack of maintainer/breakage

There is no maintainer for this package, probably not many users.
It requires effort to fix all third-party modules for this old kernel
versions. It might contain unpatched security holes.

For Pixel chromebooks, we have the samus-kernel.
Apart from that https://github.com/GalliumOS/linux might be a good choice.

pkgs/os-specific/linux/ena/default.nix

@@ -37,6 +37,5 @@ stdenv.mkDerivation rec {
     license = lib.licenses.gpl2;
     maintainers = [ lib.maintainers.eelco ];
     platforms = lib.platforms.linux;
-    broken = kernel.features.chromiumos or false;
   };
 }