Prefer defvar-keymap in some trivial cases

Prefer defvar-keymap in some trivial cases

* lisp/calendar/diary-lib.el (diary-fancy-overriding-map):
* lisp/emacs-lisp/chart.el (chart-mode-map):
* lisp/emulation/cua-base.el (cua-global-keymap)
(cua--cua-keys-keymap, cua--prefix-override-keymap)
(cua--prefix-repeat-keymap, cua--global-mark-keymap)
(cua--rectangle-keymap, cua--region-keymap):
* lisp/emulation/viper-keym.el (viper-vi-intercept-map)
(viper-insert-intercept-map, viper-emacs-intercept-map)
(viper-vi-global-user-map, viper-vi-basic-map, viper-vi-kbd-map)
(viper-vi-diehard-map, viper-insert-global-user-map)
(viper-insert-basic-map, viper-insert-diehard-map)
(viper-insert-kbd-map, viper-replace-map)
(viper-emacs-global-user-map, viper-emacs-kbd-map)
(viper-empty-keymap, viper-mode-map, viper-minibuffer-map)
(viper-ex-cmd-map, ex-read-filename-map)
(viper-slash-and-colon-map, viper-comint-mode-modifier-map)
(viper-dired-modifier-map, viper-gnus-modifier-map):
* lisp/gnus/gnus-sum.el (gnus-summary-generic-mark-map):
* lisp/menu-bar.el (global-buffers-menu-map)
(menu-bar-preferences-menu):
* lisp/mh-e/mh-e.el (mh-folder-mode-map, mh-inc-spool-map)
(mh-search-mode-map, mh-show-mode-map):
* lisp/play/dunnet.el (dungeon-batch-map):
* lisp/progmodes/autoconf.el (autoconf-mode-map):
* lisp/tool-bar.el (tool-bar-map):
* lisp/vc/ediff-help.el (ediff-help-region-map):
* lisp/vc/ediff-hook.el (menu-bar-epatch-menu)
(menu-bar-ediff-merge-menu, menu-bar-ediff-menu):
* lisp/windmove.el (windmove-mode-map):
* lisp/xwidget.el (xwidget-webkit-isearch-mode-map)
(xwidget-webkit-edit-mode-map): Prefer defvar-keymap.