[lib, keyserver, native, web] Remove the cookie field from redux

Summary:
https://linear.app/comm/issue/ENG-4377/refactor-cookie-field-in-web-redux
Removing the cookie field from redux. Adding a migration. Undoing a hack in cookieSelector.

Test Plan:
ran yarn flow-all. Since cookie was not being used since the previous diff, this should be enough

EDIT:
tested that the cookie was migrated on native:

• checked out master, opened the app, logged the cookie
• closed the app
• checked out this diff, opened the app, logged the cookie

On master, rehyderated keys included cookie. On this diff, rehydrated keys don't include 'cookie', but include the keyserverStore. Checked that cookie that was logged on master is equal to the keyserverStore.keyserverInfos['256'].cookie on this diff

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8536