revert(glittershark): "Temporarily skip grfn's subtree"

This reverts commit 475d41f698. I'd like
my derivations back, please.

Changes necessary to get this working:

- Don't depend on `nixpkgs` being in the NIX_PATH for my website - it's
  not necessary anyway since emacs 27 is mainline now
- .skip-subtrees on things that shouldn't be evaluated anyway
- Get rid of system/pkgs, and move the one thing in there that *wasn't*
  already in third_party (alsi) to third_party
- Drop notifymuch for now - it's not working, and I'll probably get it
  landed in nixpkgs before I manage to get it working
- Add __readTree = true to my systems so they get built.
- explicitly disable ci for xanthous, which is failing to build and had
  been omitted previously

Change-Id: I20f5e81d6eb7ffe040091a08d75d0cb15304f707
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1864
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

users/glittershark/gws.fyi/orgExportHTML.nix

@@ -1,22 +1,15 @@
-{ pkgs ? import <nixpkgs> {}, ... }:
+{ pkgs, ... }:
 
 with pkgs;
 with lib;
 
 let
 
-  emacs-nixpkgs =
-    (import <nixpkgs> {
-      overlays = [(import (builtins.fetchTarball {
-        url = "https://github.com/nix-community/emacs-overlay/archive/54afb061bdd12c61bbfcc13bad98b7a3aab7d8d3.tar.gz";
-        sha256 = "0hrbg65d5h0cb0nky7a46md7vlvhajq1hf0328l2f7ln9hznqz6j";
-      }))];
-    });
+  emacsWithPackages = (pkgs.emacsPackagesGen pkgs.emacs27).emacsWithPackages;
 
-  emacs = (emacs-nixpkgs.emacsPackagesFor emacs-nixpkgs.emacsUnstable)
-    .emacsWithPackages (p: with p; [
-      org
-    ]);
+  emacs = emacsWithPackages (p: with p; [
+    org
+  ]);
 
 in