[lib] Delete old replies count logic
Summary:
In the next diff we're introducing a more unified approach.
https://linear.app/comm/issue/ENG-8930/unify-the-approach-to-replies-count-and-unread-status-updates
Depends on D13057
Test Plan: Flow.
Reviewers: kamil, inka
Reviewed By: inka
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D13058