def remove_task(self, row, scan=True):
        '''删除下载任务'''
        if row[STATE_COL] == State.UPLOADING:
            self.remove_worker(row[FID_COL], stop=True)
        self.remove_task_db(row[FID_COL])
        tree_iter = row.iter
        if tree_iter:
            self.liststore.remove(tree_iter)
        if scan:
            self.scan_tasks()
删除下载任务