Remove "bin/repository lookup-users" workflow

Summary:
Ref T13552. This is one of two callsites to "diffusion.querycommits". It's an old debugging workflow which I haven't used in years and which is likely obsoleted by identities and other changes.

I believe the root problem here was also ultimately user error (a user has misconfigured their local Git author email as another user).

Test Plan: Grepped for "lookup-users", got no hits.

Maniphest Tasks: T13552

Differential Revision: https://secure.phabricator.com/D21444