zfs cannot be distributed. Disabling it in the isos.

It seems that it is a GPL violation to distribute zfs in the
installation ISOs.

https://sfconservancy.org/blog/2016/feb/25/zfs-and-linux/

If anyone knows the issue better and has a reason to reenable it
legally, feel free to reenable it. I don't know much about it.

nixos/modules/profiles/base.nix

···
   ];
 
   # Include support for various filesystems.
-  boot.supportedFilesystems = [ "btrfs" "reiserfs" "vfat" "f2fs" "xfs" "zfs" "ntfs" "cifs" ];
+  boot.supportedFilesystems = [ "btrfs" "reiserfs" "vfat" "f2fs" "xfs" "ntfs" "cifs" ];
 
   # Configure host id for ZFS to work
   networking.hostId = lib.mkDefault "8425e349";