[lib] Remove simple usages of LegacyRawThreadInfo

Summary:
Straightforward removal of LegacyRawThreadInfo where there weren't recursive flow issues.

Depends on D10198

Test Plan: Flow/CI/etc.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: rohan

Differential Revision: https://phab.comm.dev/D10209