refactor(KoohiiForm): delete obsolete mixin
refactor(KoohiiForm): delete obsolete mixin

kanji-koohii/kanji-koohii,fabd/kanji-koohii,kanji-koohii/kanji-koohii,fabd/kanji-koohii,kanji-koohii/kanji-koohii,kanji-koohii/kanji-koohii,kanji-koohii/kanji-koohii,fabd/kanji-koohii,fabd/kanji-koohii,fabd/kanji-koohii,fabd/kanji-koohii