[lib] update reduceUserInfos to return ops

Summary:
Return ops to process in on DB later.

We have two options here:

1. Return ops only when states are different - better for performance
2. Always return ops - might result in processing ops giving the same result but helps when states (redux and DB) diverge

I don't think states could be different at any point so going with option 1.

Depends on D9802

Test Plan: Just a refactor so Flow. Functionality tested later in the stack

Reviewers: tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9908