[kesyerver] Remove sessionID from website responders top level

Summary:
during https://linear.app/comm/issue/ENG-4457/refactor-sessionid-field I should have removed sessionID from top level of redux state returned from the keyserver to web client.
This field is now handled by keyserverStore.

Test Plan:
Checked that the field is not present in redux state returned from the keyserver, the app still works - it's possible to have two sessions open and a message sent in one appears
in the other. Ran yarn flow-all.

Reviewers: michal

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8922