Convert several defsubst to defun in recentf.el

Convert several defsubst to defun in recentf.el

* lisp/recentf.el (recentf-enabled-p, recentf-string-equal)
(recentf-string-lessp, recentf-push, recentf-expand-file-name)
(recentf-add-file, recentf-remove-if-non-kept)
(recentf-digit-shortcut-command-name, recentf-elements)
(recentf-menu-bar, recentf-sort-ascending)
(recentf-sort-descending, recentf-sort-basenames-ascending)
(recentf-sort-basenames-descending)
(recentf-sort-directories-ascending)
(recentf-sort-directories-descending)
(recentf-show-basenames-ascending)
(recentf-show-basenames-descending): Change from defsubst to
defun.