Could we remove the variable "tidb_enable_pseudo_for_outdated_stats" that have always been deprecated

## Bug Report

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### 1. Minimal reproduce step (Required)

This variable ”tidb_enable_pseudo_for_outdated_stats“ purpose is to replace outdated statistics with pseudo statistics when the number of table row changes exceeds a specified ratio "PseudoEstimateRatio".

However, while reorganizing the code, I discovered that:
1. This configuration was disabled three years ago due to customer issues and has never been enabled since. https://github.com/pingcap/tidb/pull/36797
2. This setting itself is unreasonable. Even if table statistics are outdated, directly falling back to pseudo statistics is extremely dangerous.

I therefore recommend deleting this configuration, along with related configurations and code.

The reference logic of this variable/config
1. related variable

2. related config only used by this variable logic

3. related const param

4. related code logic