[keyserver] Remove cookieSources

Summary:
ENG-4747
Depends on D9291

After D9290 and D9291 all cookies are from the request body so we can stop tracking this information. This diff removes cookieSources and simplifies all conditionals where it mattered.

Note: Like D9291, landing this diff will need to be defered for a while to allow older clients to migrate

Test Plan: yarn flow-all, check if web app works. Set the current web version as unsupported and check that the user gets logged out.

Reviewers: inka, kamil, atul, ashoat

Reviewed By: atul, ashoat

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9500