Adds `build_unweighted_fed_prox` to the algorithms API.
from tensorflow_federated.python.learning.algorithms.fed_avg import build_unweighted_fed_avg
from tensorflow_federated.python.learning.algorithms.fed_avg import build_weighted_fed_avg
from tensorflow_federated.python.learning.algorithms.fed_avg_with_optimizer_schedule import build_weighted_fed_avg_with_optimizer_schedule
+from tensorflow_federated.python.learning.algorithms.fed_prox import build_unweighted_fed_prox
from tensorflow_federated.python.learning.algorithms.fed_prox import build_weighted_fed_prox
from tensorflow_federated.python.learning.algorithms.fed_sgd import build_fed_sgd
