tutorial: Don't advise against cua-mode

As brudgers said in a HN comment†: "If a tutorial tutorial emphasizing
CUA makes [Emacs] adoption rates higher, the tutorial is more
successful". Not that I'm actively advocating --or even mentioning--
cua-mode, but I don't need to recommend against it for the purposes of
this tutorial.

† https://news.ycombinator.com/item?id=5732786

tutorial.haml

@@ -58,10 +58,3 @@ paste with ⌘-v, and search with ⌘-f. Still, you should eventually learn the
 Emacs alternatives for all of the above, as they are much more powerful. In
 Emacs-speak the ⌘ key is called "super", abbreviated to a lower-case "s", as in
 `s-f`.
-
-If you're not on a Mac, resist the temptation to enable cua-mode. cua-mode
-rebinds keys like `C-z`, `C-x`, `C-c`, and `C-v` to their standard Windows
-meanings. cua-mode also changes the behavior of the region, so that using
-shift-arrow keys highlights text, and typing text replaces the active
-selection, as you'd expect in most other text editors. Get used to the Emacs
-way of doing these things.