Remove compat code and functions from message.el

Remove compat code and functions from message.el

* lisp/gnus/message.el (message-send-mail-function): Remove
compat code.
(message-dont-reply-to-names, message-mode)
(message-setup-fill-variables, message-fill-paragraph)
(message-remove-blank-cited-lines, message-make-from)
(message-forward-rmail-make-body, message-tool-bar-gnome)
(message-tab): Remove compat code.
(message-completion-in-region): Remove.
(message-read-from-minibuffer): Remove compat code.