modus-themes ELPA and etc/themes

[Stefan Monnier]

I just noticed that Emacs is not aware that it comes bundled with
`modus-themes`, so it may unnecessarily fetch `modus-themes` from the GNU
ELPA archive.

The problem is due to the fact that the file is under `etc/themes` and
is hence not processed by our autoloads machinery which would otherwise
add something like

    (push (purecopy '(modus-themes 1 2 4)) package--builtin-versions)

to lisp/loaddefs.el.

There are various ways to fix this, but to me the simplest would be to
move `etc/themes` to `lisp` (or at least to move `modus-themes.el`).


        Stefan