[lib] Remove lastNavigatedTo/lastPruned from MessageStore.threads
Summary:
All of the message pruning logic is now dependent on lastNavigatedTo and lastPruned from ThreadActivityStore instead of MessageStore.threads, so instances of MessageStore.threads.[lastNavigatedTo/lastPruned]` can safely be removed.
This diff just handles removal on the "JS side." We will separately handle removal on the C++ side.
NOTE: I originally intended to migrate values from MessageStore.threads to ThreadActivityStore, but decided against it. I will still introduce a migration to remove the extraneous lastNavigatedTo and lastPruned from MessageStore.threads, but figure it makes sense to start with ThreadActivityStore empty and be populated lazily instead of immediately filling with up with entries for every thread.
Depends on D9469
Test Plan: Putting this up now, but need to do more testing before landing so marking this as DRAFT. This should all be "dead code."
Reviewers: ashoat, tomek, ginsu, rohan, kamil
Reviewed By: ashoat, kamil
Subscribers: kamil, wyilio
Differential Revision: https://phab.comm.dev/D9475