Decommission Zemke-Rhyne

Summary:
All credentials have been migrated and are now provisioned through Vault.

So long and thanks for all the fish!

Ref T930.

Test Plan: Look for zr or Zemke-Rhyne references in the repository

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T930

Differential Revision: https://devcentral.nasqueron.org/D2854