Context for why we want to revert this is in D12641. Linear task: ENG-8698

This reverts commit 51a51ba64cc988a189e843d1165a8c77ecad578f.

It's not a perfect revert, since we need to preserve the field in keyserverAuthRequestInputValidator for old clients.

To keep the field in the validator, I had to split KeyserverAuthRequest into two types, one for keyserver and one for clients.

I ran through the registration flow in my local environment and made sure it still works. I confirmed that the hash column in the users table in MariaDB is NULL