Revert "Central agent horizontal scaling spec"

This reverts commit 725a291e9c9ad1e6100f54735b2e13a64f123d13.

The initial commit was merged prematurely, before all of the
interested parties got a chance to review it. It will be
re-submitted as a fresh change.

Change-Id: Ib79af6ab62c0556511fc34f144411b5c174b8950