Prefer defvar-local in international/*.el

Prefer defvar-local in international/*.el

* lisp/international/mule-cmds.el (current-input-method)
(current-input-method-title, current-transient-input-method)
(previous-transient-input-method, input-method-history)
(deactivate-current-input-method-function)
(describe-current-input-method-function):
* lisp/international/mule.el (buffer-file-coding-system-explicit):
* lisp/international/quail.el (quail-current-package)
(quail-guidance-str, quail-overlay, quail-conv-overlay)
(quail-current-key, quail-current-str)
(quail-current-translations, quail-current-data):
* lisp/international/robin.el (robin-mode)
(robin-current-package-name): Prefer defvar-local in
international/*.el.