[lib] First pass at removing LegacyRawThreadInfo

Summary:
Part of https://linear.app/comm/issue/ENG-6366/rename-minimallyencodedrawthreadinfo-to-rawthreadinfo

We want to reduce usages of LegacyRawThreadInfo as much as possible. It should really only be around in keyserver/lib to handle old clients and in web/native to handle old migrations.

This was the first pass of removing LegacyRawThreadInfo where it was easy. Will continue trying to rip out as much of LegacyRawThreadInfo as possible.

Depends on D10625

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D10626