remove support for multi-reader dispatch queue

* Under the new postgres backed notify/listen message queue, this never
actually worked. Without using the database to store state, we can not
provide a at-most-once delivery mechanism w/ multi-readers.
* With this change, work is done ONLY on the node that requested for the
work to be done. Under rabbitmq, the node that was first to get the
message off the queue would do the work; presumably the least busy node.

awx/main/scheduler/tasks.py

@@ -5,11 +5,12 @@ import logging
 # AWX
 from awx.main.scheduler import TaskManager
 from awx.main.dispatch.publish import task
+from awx.main.dispatch import get_local_queuename
 
 logger = logging.getLogger('awx.main.scheduler')
 
 
-@task()
+@task(queue=get_local_queuename)
 def run_task_manager():
     logger.debug("Running Tower task manager.")
     TaskManager().schedule()