As my NixOS configuration kept growing, I noticed that I don't need
home-manager as much as I did before. A lot of what I need is just a way
to map nix attrsets to the program's respective configuration format,
which is something that I can now do myself, as my nix knowledge got
more extensive. After all of this, I decided to completely get rid of
home-manager, and switch to a simpler solution called hjem, which just
lets me write files to my home directory that are automatically
symlinked using `systemd-tmpfiles`.
This allows me to simplify my configuration, remove the separation
between NixOS and home-manager modules, and cut my eval times by quite a
lot (which allows for faster `nixos-rebuild switch`!).
