Allow removal of target groups from ASGs (#25126)

An empty `target_group_arns` list represents no target groups.
This is different to not passing a `target_group_arns` list at all
which can signify no change.

Remove unnecessary empty list construction, as it must already be
an empty list to get to that point.

lib/ansible/modules/cloud/amazon/ec2_asg.py

@@ -694,10 +694,8 @@ def create_autoscaling_group(connection, module):
                 module.fail_json(msg="Failed to update Autoscaling Group.",
                                  exception=traceback.format_exc(), **camel_dict_to_snake_dict(e.response))
         # Update target groups if they are specified and one or more already exists
-        elif target_group_arns and as_group['TargetGroupARNs']:
+        elif target_group_arns is not None and as_group['TargetGroupARNs']:
             # Get differences
-            if not target_group_arns:
-                target_group_arns = list()
             wanted_tgs = set(target_group_arns)
             has_tgs = set(as_group['TargetGroupARNs'])
             # check if all requested are already existing