Removes ZMQ directory
Removes ZMQ directory

This transport won't be implemented in the near future,
so it doesn't make sense to keep the directory in the code base.
This doesn't mean that the future implementation of a transport
driver for ZMQ is discarded.

Change-Id: Ia8c0b3057a34413d28dfdef99fc5dbb7100e9c50

openstack/zaqar,openstack/zaqar,openstack/zaqar,openstack/zaqar