Confusing docs about SQS long polling

[thaddock]

It's confusing to tell if long polling is supported for SQS or not. It appears from the documentation and comments that it is not enabled, but looking at the code here:
https://github.com/celery/kombu/blob/master/kombu/transport/SQS.py#L335
and:
https://github.com/celery/kombu/blob/master/kombu/async/aws/sqs/connection.py#L79
it appears to be enabled with a default of 10 seconds.

If this is correct, the confusing comments should be updated.