[lib] Refactor draft reducer

Summary:
issue: ENG-5812
We want to remove drafts of threads related to the keyservers the action was dispatched for

Test Plan: Ran the provided test, tested that when a user logs out the drafts are deleted

Reviewers: michal, kamil, ginsu

Reviewed By: michal, ginsu

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10636