[sql/keyserver] removed/edited columns affected by SIWE

Summary:
as per title we're moving the public_key to the cookies column so i dropped those columns from users and sessions.
linear task
another linear task

Test Plan: run the migration script & watch some columns disappear

Reviewers: varun, tomek, atul

Reviewed By: tomek

Subscribers: abosh, ginsu, atul, tomek, varun, ashoat

Differential Revision: https://phab.comm.dev/D5494