Update nXML to use Emacs's Unicode support, and lexical-binding

Update nXML to use Emacs's Unicode support, and lexical-binding

* etc/nxml/*.el: Remove obsolete char-name files.
* lisp/nxml/xsd-regexp.el (xsdre-range-list-difference): Remove unused
var `next'.
* lisp/nxml/rng-nxml.el (rng-set-state-after): Don't assume point-min==1.
* lisp/nxml/rng-match.el (rng-update-match-state): Simplify.
* lisp/nxml/nxml-outln.el (nxml-outline-state-transform-exceptions)
(nxml-target-section-pos, nxml-depth-in-target-section)
(nxml-outline-state-transform-alist)
(nxml-outline-display-section-tag-function): Move decl before first use.
* lisp/nxml/nxml-mode.el (nxml-char-name-ignore-case)
(nxml-char-name-alist, nxml-char-name-table)
(nxml-autoload-char-name-set-list, nxml-named-char-history): Remove vars.
(nxml-enable-char-name-set, nxml-disable-char-name-set)
(nxml-char-name-set-enabled-p, nxml-autoload-char-name-set)
(nxml-define-char-name-set, nxml-get-char-name): Remove functions.
(nxml-insert-named-char): Use read-char-by-name instead.
(nxml-char-ref-display-extra): Use get-char-code-property.
* lisp/nxml/nxml-maint.el (nxml-create-unicode-char-name-sets):
Remove function.
* lisp/nxml/nxml-glyph.el, lisp/nxml/nxml-uchnm.el: Remove files.