remove default label to fix spinning loop that wastes lots of CPU

[akrennmair]

The default label in this method serves no purpose, but causes the loop to needlessly spin, wasting lots of CPU. Removing the default label fixes this behaviour without changing the functionality of the loop itself.

[knarz]

Without the default case in the receiver, the select would block until the done channel is closed and never read any messages.

[jvatianou-connamara]

adding this to review/qa pipeline for now.