Drop RpcProxy usage from FWaaS code

This patch removes the usage of the RpcProxy compatibility class from
the FWaaS code.  The equivalent direct usage of oslo.messaging APIs
are now used instead.

Part of blueprint drop-rpc-compat.

Change-Id: I1bab4dcd376d4e9684fee1edc97fd29a61ba38de
Merge "Drop RpcProxy usage from FWaaS code"