General refactor of Doom core

- Code reduction and refactor across the board (cull unneeded minor
  advise, hooks and hacks or update them)
- Revise outdated comments and docstrings
- Reorganize core autoload libraries
- Remove large file check (Emacs already has a built-in one, which we
  augment to be even more performant when it does kick in)
- helpful.el can now be disabled completely through package!

modules/ui/doom-dashboard/config.el

@@ -66,7 +66,7 @@ Possible values:
     ("Open private configuration"
      :icon (all-the-icons-octicon "tools" :face 'font-lock-keyword-face)
      :when (file-directory-p doom-private-dir)
-     :action +default/find-in-config)
+     :action doom/open-private-config)
     ("Open user manual"
      :icon (all-the-icons-octicon "book" :face 'font-lock-keyword-face)
      :when (file-exists-p (expand-file-name "index.org" doom-docs-dir))