Remove stg fedimg's fedmsg production loopback.

This allowed staging fedimg to respond to production fedmsg messages, which was
very useful for testing.  We could try uploading the real production builds to
aws using the community credentials, and some untested fedimg code.

However, it is a pain, because in order to do its work, fedimg (staging) would
need a firewall port opened on production koji to allow it to make queries about
the createImage tasks.

Since fedimg has become stable (and staging koji has become more stable), I'm
removing this loopback, so now staging fedimg will only respond to staging
fedmsg messages from staging koji.. and it will query staging koji for more
information about those tasks.

roles/fedimg/templates/fedmsg.d/fedimg.py

@@ -22,12 +22,4 @@
 
 config = dict(
     kojiconsumer=True,
-    {% if env == 'staging' %}
-    # Establish a loop from production back into the staging instance.
-    endpoints = {
-        "production-loopback": [
-            "tcp://hub.fedoraproject.org:9940",
-        ],
-    },
-    {% endif %}
 )