pendalf89\filemanager\models\Tag::removeUnusedTags PHP Method

    public static function removeUnusedTags()
    {
        return Yii::$app->db->createCommand('DELETE filemanager_tag
			FROM
				filemanager_tag
			LEFT JOIN filemanager_mediafile_tag ON id = tag_id
			WHERE
				ISNULL(mediafile_id)')->execute();
    }

 public function afterSave($insert, $changedAttributes)
 {
     parent::afterSave($insert, $changedAttributes);
     Tag::removeUnusedTags();
 }