Ref T2543. These are the last ArcanistDifferentialRevisionStatus callsites.

This removes the very old legacy precommitRevisionStatus field, which has no other readers. This was obsoleted by the CLOSED_FROM_ACCEPTED stuff, but retained for compatibility.

• Poked these with the test console, although they're a little tricky to be sure about.
• Grepped for ArcanistDifferentialRevisionStatus, no more hits.