Remove some unnecessary calls to mh-funcall-if-exists

Remove some unnecessary calls to mh-funcall-if-exists

* lisp/mh-e/mh-acros.el (mh-do-at-event-location):
* lisp/mh-e/mh-mime.el (mh-mime-cleanup, mh-display-smileys)
(mh-insert-mime-security-button, mh-insert-mime-button):
* lisp/mh-e/mh-show.el (mh-defun-show-buffer):
* lisp/mh-e/mh-xface.el (mh-x-image-url-fetch-image)
(mh-x-image-display, mh-picon-image-types): Remove unnecessary calls
to mh-funcall-if-exists; these functions always exist as they are
autoloaded.