Convert some keymaps to defvar-keymap

Convert some keymaps to defvar-keymap

* lisp/simple.el (special-mode-map):
* lisp/net/shr.el (shr-map):
* lisp/net/eww.el (eww-link-keymap):
(eww-mode-map):
(eww-submit-map):
(eww-bookmark-mode-map):
(eww-history-mode-map):
(eww-buffers-mode-map):
* lisp/gnus/message.el (message-mode-map): Use defvar-keymap.

* lisp/gnus/gnus-eform.el (gnus-edit-form-mode-map):
* lisp/gnus/gnus-dired.el (gnus-dired-mode-map):
* lisp/gnus/gnus-bookmark.el (gnus-bookmark-bmenu-mode-map): Use
defvar-keymap.

* lisp/gnus/gnus-group.el (gnus-group-mode-map): Use define-keymap.

* lisp/gnus/gnus-html.el (gnus-html-image-map): Use defvar-keymap.

* lisp/gnus/gnus.el: Autoload gnus-score-edit-all-score.