Remove some more MH-E compat code

Remove some more MH-E compat code

* lisp/mh-e/mh-acros.el (defun-mh, defmacro-mh): Make obsolete.

* lisp/mh-e/mh-gnus.el (mh-gnus-local-map-property): Make obsolete.
* lisp/mh-e/mh-mime.el (mh-insert-mime-security-button)
(mh-insert-mime-button): Don't use above obsolete function.

* lisp/mh-e/mh-gnus.el (mh-mm-text-html-renderer): Make obsolete.
* lisp/mh-e/mh-mime.el (mh-mm-inline-media-tests)
(mh-signature-highlight): Remove references to removed Gnus
variable 'mm-inline-text-html-renderer'.

* lisp/mh-e/mh-letter.el (mh-letter-complete): Make into obsolete
function alias for 'completion-at-point'.  Update callers.

* lisp/mh-e/mh-e.el (mh-inc-spool-list, mh-show-use-xface-flag):
* lisp/mh-e/mh-comp.el (mh-ascii-buffer-p):
* lisp/mh-e/mh-show.el:
* lisp/mh-e/mh-utils.el: Remove some references to XEmacs.

* lisp/mh-e/mh-comp.el (mh-send-letter): Remove XEmacs and Emacs
compat code.

* lisp/mh-e/mh-compat.el (mh-display-completion-list): Remove
compat code for Emacs 22 and earlier.

* lisp/mh-e/mh-e.el (mh-inherit-face-flag)
(mh-min-colors-defined-flag): Make XEmacs and Emacs 21 compat
variables obsolete.
(mh-face-data): Adjust to assume above variables are always t.

* lisp/mh-e/mh-mime.el (mh-mime-button-map): Remove XEmacs and
Emacs 20 compat code.

* lisp/mh-e/mh-utils.el (mh-mapc): Make Emacs 20 compat function
into obsolete function alias for mapc.  Update callers.

* lisp/mh-e/mh-xface.el (mh-show-xface-function, mh-show-xface):
Remove Emacs 20 compat code.