change plan for insert without unique key column

[ouyuanning]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue https://github.com/matrixorigin/MO-Cloud/issues/2567

What this PR does / why we need it:

当insert语句中，没有包含unique key的列时。
现在MO会做一次去重检查和insert操作，跟莫尘讨论了下，应该这部分可以去掉。

--这种不需要给b这个隐藏表做去重,也不写隐藏表
create table t(a int, b int unique key);
insert into t(a) select * from x;
insert into t (a) values (1); 


--但是以下情况需要去重
create table t(a int, b int unique key default 0);
create table t(a int, b int unique key auto_inrement);
insert into t(a) values (1);
insert into t(a) select * from x;