Materialize with "ignore" behavior introduce incorrect data

[TennyZhuang]

Describe the bug

When executing an insert-after-delete case, the implementation is wrong. It forgot to delete the value in the cache.

The input stream:

+ 1 3
- 1 3
+ 1 6

The table data:

1 -> 3

A key can never been updated in this mode.

Error message/log

No response

To Reproduce

The testcase was added in #14345, and I'll fix the bug in that PR.

Expected behavior

1 -> 6

How did you deploy RisingWave?

No response

The version of RisingWave

v1.5.4

Additional context

No response

[TennyZhuang]

The behavior is never used, so priority/critical was removed.