Remove some XEmacs compat code from tree-widget.el

* lisp/tree-widget.el (tree-widget-themes-load-path)
(tree-widget-use-image-p, tree-widget-create-image)
(tree-widget-image-formats, tree-widget-image-properties)
(tree-widget-lookup-image): Remove XEmacs compat code.
1 job for master in 55 minutes and 26 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed #3675
test-all

00:55:26