Clean up binary api message handler registration issues

Removed a fair number of "BUG" message handlers, due to conflicts with
actual message handlers in api_format.c. Vpp itself had no business
receiving certain messages, up to the point where we started building
in relevant code from vpp_api_test.

Eliminated all but one duplicate registration complaint. That one
needs attention from the vxlan team since the duplicated handlers have
diverged.

Change-Id: Iafce5429d2f906270643b4ea5f0130e20beb4d1d
Signed-off-by: Dave Barach <dave@barachs.net>