Use lexical-binding in recentf.el

Use lexical-binding in recentf.el

* lisp/recentf.el: Use lexical-binding.  Doc fix.
(recentf-save-file): Strength reduce 'eval' to 'symbol-value'.
(recentf-trunc-list): Make into obsolete function alias for
'seq-take'.  Update callers.
(recentf-show-file-shortcuts-flag): Doc fix.
(recentf-menu-elements, recentf-make-menu-items)
(recentf-make-menu-item, recentf-dialog-mode-map)
(recentf-dialog, recentf-open-files-item)
(recentf-open-files-items, recentf-open-files)
(recentf-load-list): Quote function symbols as such.
(recentf-relative-filter, recentf-file-name-nondir): Remove
redundant #' before lambda.