Remove compute 2.x rpc api

A previous change adding support for the 3.x rpc interface but retained
compatibility with 2.x as a transition point.  This commit removes the
old API from the server side.

UpgradeImpact

Part of blueprint rpc-major-version-updates-icehouse

Change-Id: I31c21055163e94b712d337568b16b9b7a224b52f