[lib] Remove all remaining instances of LegacyRelativeMemberInfo from codebase

Summary:
Part of ENG-6366 : Rename MinimallyEncodedRawThreadInfo to RawThreadInfo

Depends on D10728

Test Plan: flow

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10729