Move password-word-equivalents defn to mule-conf

Move password-word-equivalents defn to mule-conf

* lisp/international/mule-conf.el (password-word-equivalents):
Move here ...
* lisp/simple.el (password-word-equivalents): ... from here.
This variable belongs in an i18n file somewhere, not in simple.el,
since it’s i18n-related.  Also, having it in simple.el tickles
Emacs performance bugs on some platforms when developers visit
simple.el.  Problem reported by Drew Adams in, for example:
https://lists.gnu.org/r/emacs-devel/2018-04/msg00124.html