Declare compat macro mh-do-in-gnu-emacs obsolete

Declare compat macro mh-do-in-gnu-emacs obsolete

* lisp/mh-e/mh-acros.el (mh-do-in-gnu-emacs): Declare compat macro
obsolete.
* lisp/mh-e/mh-compat.el (mh-require):
* lisp/mh-e/mh-folder.el (mh-folder-mode):
* lisp/mh-e/mh-letter.el (mh-letter-mode):
* lisp/mh-e/mh-mime.el (mh-mime-button-map)
(mh-mime-security-button-map, mh-small-image-p)
(mh-signature-highlight):
* lisp/mh-e/mh-show.el (mh-show-mode):
* lisp/mh-e/mh-tool-bar.el (mh-tool-bar-define):
* lisp/mh-e/mh-utils.el (mh-logo-display)
(mh-hidden-header-keymap):
* lisp/mh-e/mh-xface.el (mh-face-display-function)
(mh-picon-image-types, mh-x-image-display): Don't wrap code in
compat macro 'mh-do-in-gnu-emacs'.