refactor!(org): +pretty: use org-modern instead

BREAKING CHANGE: This changes the packages that +pretty depends on;
removing org-superstar and org-fancy-priorities, and replacing them with
org-modern. The user doesn't need to do anything but remove any
now-defunct configuration for org-superstar and org-fancy-priorities
from their config.

This was done to simplify our config, lighten our maintenance burden,
and rely on a more reliable (and still-maintained) package.

Fix: #6434

modules/lang/org/contrib/pretty.el

@@ -4,31 +4,11 @@
   (setq org-highlight-latex-and-related '(native script entities)))
 
 
-(use-package! org-superstar ; "prettier" bullets
-  :hook (org-mode . org-superstar-mode)
-  :config
-  ;; Make leading stars truly invisible, by rendering them as spaces!
-  (setq org-superstar-leading-bullet ?\s
-        org-superstar-leading-fallback ?\s
-        org-hide-leading-stars nil
-        org-superstar-todo-bullet-alist
-        '(("TODO" . 9744)
-          ("[ ]"  . 9744)
-          ("DONE" . 9745)
-          ("[X]"  . 9745))))
-
-
-(use-package! org-fancy-priorities ; priority icons
-  :hook (org-mode . org-fancy-priorities-mode)
-  :hook (org-agenda-mode . org-fancy-priorities-mode)
-  :config
-  (setq org-fancy-priorities-list '("⚑" "⬆" "■"))
-  ;; HACK: Prevent org-fancy-priorities from interfering with org exporters or
-  ;;   other non-interactive Org crawlers/parsers (see #8280).
-  (defadvice! +org--inhibit-org-fancy-in-non-real-buffers-a (&rest _)
-    :before-until #'org-fancy-priorities-mode
-    org-inhibit-startup))
-
-
-(use-package! org-appear ; better markup edit
+(use-package! org-appear
   :hook (org-mode . org-appear-mode))
+
+
+(use-package! org-modern
+  :hook (org-mode . org-modern-mode)
+  :hook (org-agenda-finalize . org-modern-mode)
+  :hook (org-modern-mode . +org-pretty-mode))