Prefer defvar-keymap in vc/*.el

Prefer defvar-keymap in vc/*.el

* lisp/vc/add-log.el (change-log-mode-map):
* lisp/vc/ediff-mult.el (ediff-dir-diffs-buffer-map):
* lisp/vc/vc-annotate.el (vc-annotate-mode-map):
* lisp/vc/vc-bzr.el (vc-bzr-shelve-map):
* lisp/vc/vc-dir.el (vc-dir-status-mouse-map)
(vc-dir-filename-mouse-map):
* lisp/vc/vc-git.el (vc-git-stash-shared-map, vc-git-stash-map)
(vc-git-stash-button-map, vc-git-log-edit-mode-map):
* lisp/vc/vc-hg.el (vc-hg-log-edit-mode-map)
(vc-hg-extra-menu-map):
* lisp/vc/vc-hooks.el (vc-prefix-map): Prefer defvar-keymap.