Removed all feedback code.

## Enhancement
This is an experimental feature and we decided to remove it now.

The argument has been removed in v6.2.0. See: [docs.pingcap.com/zh/tidb/stable/release-6.2.0#%E9%85%8D%E7%BD%AE%E6%96%87%E4%BB%B6%E5%8F%82%E6%95%B0](https://docs.pingcap.com/zh/tidb/stable/release-6.2.0#%E9%85%8D%E7%BD%AE%E6%96%87%E4%BB%B6%E5%8F%82%E6%95%B0)

So we can safely remove it now.