Use emacsUnstable overlay instead of mine

Less work for me!

modules/editors/emacs.nix

@@ -16,7 +16,7 @@ with lib;
     my = {
       packages = with pkgs; [
         ## Doom dependencies
-        my.emacs27
+        emacsUnstable
         git
         (ripgrep.override {withPCRE2 = true;})
 

packages/default.nix

@@ -6,7 +6,6 @@
         (callPackage
           (builtins.fetchTarball
             https://github.com/xzfc/cached-nix-shell/archive/master.tar.gz) {});
-      emacs27 = (callPackage ./emacs27.nix {});
       linode-cli = (callPackage ./linode-cli.nix {});
       ripcord = (callPackage ./ripcord.nix {});
       zunit = (callPackage ./zunit.nix {});

packages/emacs27.nix

@@ -1,19 +0,0 @@
-# https://github.com/nix-community/emacs-overlay is all about Emacs HEAD and
-# pkgs.emacs is all about stable, but I want 27.0.90 with its native JSON
-# library, and none of HEAD's instability, so...
-
-{ stdenv, pkgs, lib, fetchurl, ... }:
-
-pkgs.emacsGit.overrideAttrs (oa: rec {
-  name = "emacs-${version}";
-  version = "27.0.90";
-  src = fetchurl {
-    url = "https://alpha.gnu.org/gnu/emacs/pretest/${name}.tar.xz";
-    sha256 = "1x0z9hfq7n88amd32714g9182nfy5dmz9br0pjqajgq82vjn9qxk";
-  };
-  buildInputs = oa.buildInputs ++ [ pkgs.jansson ];
-  configureFlags = oa.configureFlags ++ [ "--with-jansson" ];
-
-  # Remove tramp-detect-wrapped-gvfsd.patch because it doesn't work with 27.0.90
-  patches = lib.drop 1 oa.patches;
-})