Redux migration to remove messageStore.threads[threadID].[lastPruned/lastNavigatedTo].
We don't **really* need this since messageStore.threads is persisted by both Redux and SQLite so the SQLite SET_MESSAGE_STORE will override the messageStore.threads that were REHYDRATED as soon as the app is first opened anyways, but figure it doesn't hurt.
Depends on D9517
Then why are we keeping styles like border and border-radius?
Don't these styles also affect the <textarea> tag? Are you sure we want to be removing these styles for that as well? Or should we break this into two separate selectors (one for input and another for textarea)?