Rip LegacyThreadInfo out of selectors and related code
Summary:
Ripped LegacyThreadInfo out of selectors and updated related code to use ThreadInfo as well.
We're now down to 6 usages of LegacyThreadInfo from ~750
WARNING: There was one instance where we had to add noop branching to web/modals/threads/settings/thread-settings-modal.react.js:68-72 to appease flow.
Depends on D10140
Test Plan: CI/flow/etc.
Reviewers: ashoat, ginsu, tomek, rohan
Reviewed By: ashoat
Differential Revision: https://phab.comm.dev/D10142