[keyserver] Stop accepting http cookies

Summary:
ENG-4747
Depends on D9290

We are no longer sending http cookies from the web app, so we can stop accepting them. Note: that means that web clients will need to reload to run the cookie migration.

Test Plan: Check that the web app works and that the websocket connects

Reviewers: inka, kamil, atul, ashoat, tomek

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9291