新增竞赛相关的数据表中，外键关联没有添加同步更新和删除

[Pipepw]

这是我再idea上运行web程序出现的问题，因为外键关联，所以在执行删除操作时，会报错，从而导致删除失败，报错信息如下：
Cannot delete or update a parent row: a foreign key constraint fails (voj.voj_contest_submissions, CONSTRAINT voj_contest_submissions_ibfk_2 FOREIGN KEY (submission_id) REFERENCES voj_submissions (submission_id)) at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:117) ~[mysql-connector-java-8.0.16.jar:8.0.16]

[node]

为了方便系统扩展，建议取消所有外键，不然扩展起来太尴尬了 :)