Updates callsites to use default_num_clients instead of num_clients, in preparation for parameter name change.
Updates callsites to use default_num_clients instead of num_clients, in preparation for parameter name change.

PiperOrigin-RevId: 369985467
Change-Id: I51430aad8553ddc92afb772ccb207aa8fefa5149

google-research/federated,google-research/federated