npm: Use home-manager package instead of nixos module

Now that I am able to understand and read NixOS/nixpkgs source code, I
understand that the usage of the npm module isn't needed since I don't
configure npm at a global level.

home/neovim.nix

@@ -22,6 +22,7 @@ in
     nixpkgs-fmt
     nixfmt
     nodejs
+    npm
     yarn
     deno
     gcc

src/main.nix

@@ -29,8 +29,6 @@ let VARIABLES = import ./variables.nix; in {
   hardware.opengl.driSupport32Bit = true;
 
   programs.neovim.enable = true;
-  programs.npm.enable = true;
-
   environment.systemPackages = with pkgs; [
     hypr-contrib.packages."${VARIABLES.system}".grimblast
     nix-gaming.packages."${VARIABLES.system}".osu-stable