Remove undo-tree

Also remove the `queue' dependency.

Nowadays `vundo' is a better choice, but I don't want to force that on
anyone, so assimilate neither `vundo' not `undo-tree' in this branch.

.gitmodules

@@ -43,18 +43,12 @@
 [submodule "no-littering"]
 	path = lib/no-littering
 	url = https://github.com/emacscollective/no-littering.git
-[submodule "queue"]
-	path = lib/queue
-	url = https://git.savannah.gnu.org/git/emacs/elpa.git
 [submodule "transient"]
 	path = lib/transient
 	url = https://github.com/magit/transient.git
 [submodule "treepy"]
 	path = lib/treepy
 	url = https://github.com/volrath/treepy.el.git
-[submodule "undo-tree"]
-	path = lib/undo-tree
-	url = https://github.com/tarsiiformes/undo-tree.git
 [submodule "with-editor"]
 	path = lib/with-editor
 	url = https://github.com/magit/with-editor.git

init.el

@@ -155,11 +155,6 @@
   :defer t
   :config (cl-pushnew 'tramp-own-remote-path tramp-remote-path))
 
-(use-package undo-tree
-  :config
-  (global-undo-tree-mode)
-  (setq undo-tree-mode-lighter ""))
-
 ;;; Tequila worms
 
 (borg--load-config (concat (user-real-login-name) ".el"))