[lib] Refactor logout in thread activity reducer

Summary:
issue: ENG-5827
We want to remove only the threads related to the keyservers the user is disconnecting from

Test Plan: Ran the provided test

Reviewers: michal, kamil, ginsu

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10661