(quail-japanese-update-translation): Adjusted for the change of
quail-update-translation. Now this function should return
CONTROL-FLAG.
(quail-japanese-toggle-kana): Update quail-conversion-str.
(quail-japanese-kanji-kkc): Likewise.
(quail-japanese-switch-package): Reset quail-current-str and
quail-conversion-str.