Reroute all RefQuery callers to HardpointEngine

Summary:
Ref T11968. "arc browse", "arc branch", and "arc diff" currently may execute into the RefQuery engine. Reroute them to the HardpointEngine.

This removes older-generation "Ref" objects and renames the replacement "RefPro" objects to "Ref".

Test Plan: Ran "arc branch", "arc browse <various things>", "arc diff", searched for affected symbols.

Maniphest Tasks: T11968

Differential Revision: https://secure.phabricator.com/D21082