[lib] Remove branching from threadInfoFromRawThreadInfo(...)

Summary:
Part of threadInfoFromRawThreadInfo(...).

Required changes to createPendingThread and sendPushNotifs.

Depends on D10715

Test Plan: flow, will make sure push notifs continue to work as expected.

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10718