Prefer defvar-keymap and keymap-set in recentf.el

* lisp/recentf.el (recentf-mode-map): Prefer defvar-keymap.
(recentf--shortcuts-keymap): Prefer keymap-set.
1 job for master in 4 minutes and 7 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Normal
passed #48081
test-lisp-inotify

00:04:07