[lib] Remove ThreadInfo alias for [Legacy/MinimallyEncoded]ThreadInfo

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

We've now replaced all instances of the ThreadInfo alias so we can rip it out. In next diff we will rename MinimallyEncodedThreadInfo to ThreadInfo.

Depends on D10641

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10642