simplify dynamic queue binding

we recently made a change so that instances no longer bind to
instance-group specific queues, but now instead they each bind to
a direct queue for their specific hostname
(https://github.com/ansible/tower/pull/1922)

Because of this, we shouldn't *need* to reconfigure the queue binds at
runtime anymore when group membership changes. Under our new model,
every celeryd listens on a queue named after its hostname; when the
scheduler finds a task to run, it picks an Instance in the target
Instance Group and sends the task to the queue for that Instance's
hostname.

awx/main/models/ha.py

@@ -212,6 +212,8 @@ class InstanceGroup(BaseModel, RelatedJobsMixin):
     def fit_task_to_most_remaining_capacity_instance(self, task):
         instance_most_capacity = None
         for i in self.instances.filter(capacity__gt=0).order_by('hostname'):
+            if not i.enabled:
+                continue
             if i.remaining_capacity >= task.task_impact and \
                     (instance_most_capacity is None or
                      i.remaining_capacity > instance_most_capacity.remaining_capacity):