Remove Instance Group concept/usage from WorkflowJobs

This also relaxes some of the task manager rules on Instance Groups
down the full stack such that workflow jobs tend to shortcut the
processing or omit it altogether.

This lets the workflow job spawning logic exist outside of the
instance group queues, which it doesn't need to participate in in the
first place.

awx/main/managers.py

@@ -178,8 +178,6 @@ class InstanceGroupManager(models.Manager):
             if t.status == 'waiting' or not t.execution_node:
                 # Subtract capacity from any peer groups that share instances
                 if not t.instance_group:
-                    logger.warning('Excluded %s from capacity algorithm '
-                                   '(missing instance_group).', t.log_format)
                     impacted_groups = []
                 elif t.instance_group.name not in ig_ig_mapping:
                     # Waiting job in group with 0 capacity has no collateral impact