Remove zmq-receiver from setup.cfg

In commit 1a91aac we removed the zmq-receiver script (in favor of
oslo-messaging-zmq-receiver) but forgot to remove the entry from
setup.cfg.

Closes-Bug: #1279739
Change-Id: Icd08a5b28daee7234abd24ba502c56cc00abcb8c
Merge "Remove zmq-receiver from setup.cfg"