Remove more MH-E compat code

Remove more MH-E compat code

* lisp/mh-e/mh-e.el (mh-strip-package-version, defgroup-mh)
(defcustom-mh, defface-mh): Make Emacs 21 compat aliases obsolete.
Update callers.

* lisp/mh-e/mh-e.el:
(mh-exchange-point-and-mark-preserving-active-mark)
* lisp/mh-e/mh-folder.el (desktop-buffer-mode-handlers):
* lisp/mh-e/mh-mime.el (mh-mm-inline-media-tests)
(mh-have-file-command, mh-mime-security-button-map):
* lisp/mh-e/mh-show.el (mh-summary-height):
* lisp/mh-e/mh-speed.el (mh-process-kill-without-query):
* lisp/mh-e/mh-xface.el (mh-uncompface-executable)
(mh-face-to-png, mh-uncompface, mh-picon-file-contents): Remove
XEmacs and Emacs 21 and older compat code.