Move avy, ace-link & ace-window out of core

They don't belong there, and ace-window is no longer a core dependency
anyhow.

modules/app/twitter/autoload.el

@@ -82,6 +82,7 @@ that works with the feature/popup module."
 (defun +twitter/ace-link ()
   "Open a visible link, username or hashtag in a `twittering-mode' buffer."
   (interactive)
+  (require 'avy)
   (let ((pt (avy-with +twitter/ace-link
               (avy--process
                (+twitter--collect-links)

modules/app/twitter/packages.el

@@ -2,3 +2,4 @@
 ;;; app/twitter/packages.el
 
 (package! twittering-mode)
+(package! avy)